Version tested DigitalFoundry
One of the most anticipated graphics card releases of the year, the GTX 660 Ti is NVIDIA's first entry in the mid-range price bracket to feature their powerful Kepler architecture. The promise is a grand one; even early leaks of its specifications revealed it would be offering the very same core and memory clock speeds seen in the pricier GTX 670 model. The confirmed starting retail price of the card is set at £249 - though we're already seeing drops lower in places. It's a cut of roughly £40-£50, but at what cost to the card's raw performance?
Looking at the specs, the only major change being made here is to the GTX 660 Ti's memory interface, which is shortened from a 256-bit bus to just a 192-bit one for its reference release, which has the unfortunate consequence of taking out an entire ROP unit too. All other factors remain precisely the same; the 2GB of GDDR5 RAM is still clocked at a staggering 6008MHz, and the 915MHz core clock and [Corrected] 1344 CUDA cores are thankfully unaffected in the transition. During our Digital Foundry review of the GTX 670, we found that cut-backs from the GTX 680 were pretty conservative, and in terms of the gameplay experience, in many titles you'll have trouble discerning any kind of difference between this and its more expensive sibling.
The impact the decrease in bandwidth is easily measurable by the card's fill-rate - the number of pixels that the card can render per second. We test the difference on a factory overclocked GTX 660 Ti 'Power Edition' from MSI, where the resulting memory bandwidth is calculated at just 144.2GBps. Compared to the 192.0GBps throughput possible on a stock GTX 670, this limitation primarily effects users intending to use higher resolutions or multiple passes of multi-sample anti aliasing in their games.
There are some key differences to this version of the card and the standard model. For starters, the core clock is bumped up from 915MHz to 1020MHz, while the boost mode clock - should there be power to spare - is capable of hitting 1098MHz. This comes at a cost to its rated TDP, which is reduced to a respectable 150 watts for the generic model, whereas this particular card is rated at 190 watts - putting it in a similar ballpark to the older Fermi cards. This means that two 6-pin PCIe connectors are still necessary to drive the card properly. NVIDIA has given carte blanche to its partners to overclock the standard design, so expect to see plenty of overclocked variants. It's worth noting that our card has no memory overclock - it may be worth your while looking out for a variant where this is taken care of for you as it should go some way in overcoming the bandwidth challenges imposed by the narrower 192-bit bus.
"The GTX 660 Ti is effectively identical to the monster GTX 670 with just two major differences - memory bus drops down to 192-bit from 256-bit, impacting bandwidth significantly, while a ROP unit has also been removed."
The build quality of our overclocked MSI unit feels very sturdy overall, and we notice no flex present while installing. The front plastic frame used to hold the cooling system can feel flimsy while handling some non-OEM cards, but this doesn't prove to be a problem at all here; the frame is bolted tightly to the PCB itself by four screws. Contained within it is the Frozr IV cooling system, taking the form of two 8cm fans that connect with a large aluminium fin array. This stretches across almost the entirety of the card's length, and at the bottom, we see four cooling pipes tucked around the front of its full PCIe 3.0 interface.
The thermal output is exceedingly low as a result. In fact, we don't hear the fans kick into their highest RPM preset during even sustained benchmarking sessions, and our heat sensor reads no greater than 55 degrees Celsius at peak. It's a markedly quieter card than the reference GTX 670 too, which continues to create a faint, high-pitched whirr the moment any kind of gameplay begins. Here, we see the card achieve superior clocks through the use of a higher quality cooling array, which happens to stay very close to silent.
Turning it to its end, we see a flexible range of ports to work with that are identical to its more prestigious siblings. On the top row we have a dual link DVI-D, while on the bottom we see a DVI-I, and also means for DisplayPort 2.1 and HDMI connections. Just as with all entries in the GTX 6xx series, the card also runs up to four displays simultaneously, or three stereo 3D displays if you can afford all the necessary kit.
GTX 660 Ti: Performance Analysis
For our tests, we plant the GTX 660 Ti into our high-end PC. This setup features an Intel i5-2500k processor overclocked to 4.2GHz, coupled with 8GB of 1600MHz RAM, which should remove any potential bottlenecks getting in the way of accurate GPU results. For comparison, we also test another factory overclocked card: the HD 7850 'IceQ Turbo X' from HIS, which at around £200, is a small step down the mid-range price bracket the GTX 660 Ti is shooting for.
For an extreme perspective on performance-per-pound, we include the the low-end HD 6870 card in our tests too, which currently retails around the £100 mark or thereabouts, offering a sublime sweetpoint in terms of price vs. performance.
For Metro 2033 and Batman Arkham City, we run their respective in-game benchmark tools at a resolution of 1920x1080, with very high graphical settings, and DirectX 11 features such as tessellation enabled. To keep the tests consistent across both NVIDIA and AMD brands, we uncheck the PhysX boxes, and add the maximum level of multi-sample anti aliasing possible in either case - 4x for Metro 2033, and 8x for Arkham City. Naturally, we disengage v-sync to make sure there's no ceiling for the frame-rate, should it rise above the 60Hz refresh of our display.
"Our benchmarking table illustrates nicely the difference in performance you can expect from what we would consider as the best £100, £200 and £250 graphics cards."
|HD 6870||HD 7850||GTX 660 Ti|
|Metro 2033 Average FPS||18.67||23.33||25.08|
|Batman AC Average FPS||48.00||51.00||60.00|
|3DMark 11 Score||X1393/P4441||X1647/P5492||X2854/P8500|
|3D Mark 11 Graphics||1244/4133||1473/5534||2631/8937|
It turns out that neither of these games can quite surpass 60FPS on average, but the 660 Ti does hit this number right on the nose. This is an impressive turnaround given the fears we had over the restricted memory bus, bearing in mind that high levels of MSAA could saturate the bandwidth available. Here we see a lead of approximately 20 per cent for demanding Unreal Engine 3 games like Arkham City, although the lead isn't nearly as pronounced for the Metro test, where it's barely 2FPS ahead.
In the case of 4A Studios' game, the sheer number of concurrent light sources, animated enemies and fire effects simply brings most cards to their knees - particularly for the opening third of the fly-through. NVIDIA's latest card does near close enough to the 30FPS mark on average to make this perceptibly smooth, but the fluctuations when the cannisters explode would make actual gameplay experience untenable.
To round out the benchmarks, we use the 3DMark 11 toolset which has become synonymous with gauging the proficiency of DirectX 11 compatible cards. Here we run through a gamut of synthetic tests which push hard on tessellation and physics-based tasks, and we see a very wide gap begin to form between the three cards. On the Extreme preset running at full 1920x1080 resolution, we find the overclocked GTX 660 Ti delivers over twice the overall score achieved on the HD 6870. The HD 7850 fares a little better by comparison, but the gap still remains substantial between the two, and certainly more so than the preceding gameplay tests.
Gameplay Analysis: Video Benchmarks
For the next round of tests, we pit these cards against each other in matching gameplay scenarios. As always, we pick the more demanding DirectX 11 titles such as Battlefield 3 and Crysis 2 to get an idea of how they cope with the API's latest tricks, while a test of The Elder Scrolls V: Skyrim gives us an overview of how these cards cope with large sandbox-style games.
We're firm believers in image consistency during gameplay, so v-sync is engaged, eliminating tearing. This can affect performance in different ways - frame-rate is capped at 60FPS, while challenging areas can see a performance hit as "over budget" frames need to wait until the next screen refresh in order to be displayed. However, in our book, screen-tear on an enthusiast level PC shouldn't be tolerated unless you're a pro-gamer looking for the absolute minimum in terms of input lag.
"With only minor tweaks to Battlefield's quality settings, the GTX 660 Ti can achieve a sustained, perceptual 60FPS performance level at ultra - impressive stuff for a £250 graphics card."
First up, we run Battlefield 3 at ultra settings across the board, and with a resolution of 1920x1080 to tax the fillrate on the GTX 660 Ti. This includes the higher 4x MSAA settings in conjunction with high quality FXAA, with the former being the biggest culprit for performance drops out of all the variables available. We follow our standard loop around the Operation Swordbreaker level, where the skirmishes around derelict car parks and war-torn highways pose a bigger challenge to sustaining 60FPS than any other campaign stage.
True enough, the frame-rate sticks like glue to the 50FPS line on the GTX 660 Ti for much of the way through the initial market section, which is an impressive feat considering it's completely maxed out, though not ideal for players demanding the very best levels of response. The same bar for performance holds true during the two major outdoor battles, though instances where lines of vehicles explode can tug this straight down to the 30FPS line. This is still put in very positive light when compared to the overclocked HD 7850, which can barely stay afloat of the 40FPS mark during matching sections. Alas, the HD 6870 isn't suited to these settings at all, preferring to lock itself to 30FPS during battle, and lower during these moments of high demand.
Moving on to Crytek's flagship shooter, we find the introductory sequence in the submarine to be the heaviest hitter due to the excess of water and particle effects. As before, all settings are maxed out at extreme with the resolution set to 1080p.
"Crytek's ultra quality settings prove too much for all of the GPUs we tested here, with none of them able to sustain 1080p60 - though overall the GTX 660 Ti proves to be good value for its £50 premium."
Performance isn't quite optimal for either the GTX 660 Ti or HD 7850 here - though funnily enough we do see long flourishes of 60FPS playback for the former during the battle sequence. This may owe itself to the New York skyscrapers acting as occluders, limiting the overall field of view during this enclosed area. For the rest of play, such as the long view over the harbours from above, we're seeing fluctuations between 40 and 50FPS on these cards - though always in favour of NVIDIA's offering.
Much of this will have to do, once again, with the combination of anti-aliasing and this higher resolution. The demands put on the card's fill-rate are having a direct impact on performance, and dropping this setting immediately improves this juddering state of affairs. The HD 6870 suffers at these higher settings once again however, only this time it dips below our performance grid into sub-20FPS territory during cut-scenes, for example, during the bridge collapse section.
All three cards fare much better in The Elder Scrolls V: Skyrim, where, despite having all settings maxed out on ultra, the use of native DirectX 9 alleviates some of the demands imposed by the previous two games. It's here that we find the GTX 660 Ti comes into its own with an impeccable 60FPS performance, while the HD 7850 achieves similar results for much of the downhill trail, only with occasional dips to 55FPS. The irregularity of these dips means it amounts to a perceptual 60FPS, which is a great achievement for the card considering it's powered by a single 6-pin PCIe cable, and runs with a TDP of 150w.
"In our test, Skyrim manages to stay locked at 60 frames per second from start to finish on the new graphics card, even in the NPC intensive areas."
The downward route to Helgen village doesn't play out quite so handsomely for our HD 6870, which suffers for too often lurking in the 40FPS mire - but once it's gone beyond this section it enjoys a clear stretch at the maximum potential frame-rate. This represents one of the most challenging sequences of play in the game, due to the uncommon number of NPCs condensed on-screen at once. For this card, the rest of the Skyrim is entirely playable at these settings at above 30FPS, but it doesn't offer the sheer consistency of performance possible with the GTX 660 Ti.
Overall what we find when comparing our three test GPUs is best-in-class performance at each of their respective price-points. The GTX 660 Ti at around £240-£250 is clearly gunning for the Radeon HD 7870, where we would expect to see a much more interesting battle with NVIDIA's new entrant.
Gameplays Analysis: The Best of the Rest
To get a broader impression of how each of these cards perform, we put aside the "big three" and take a cursory look at some other less demanding classics on the platform. Many of these easily fire through the 60FPS ceiling, so for these tests we choose to disengage v-sync to show the full extent of their capabilities. Besides this, all games are running at maximum settings at 1920x1080, with every graphical feature checked besides PhysX. If there's an option for MSAA, we also choose 2x in every case as this is usually sufficient for removing edge artifacting at this higher resolution.
To kick off, we take a loop around the Cold Boot chapter of Portal 2 which has us puzzling though a sequence of mid-game areas, and which do little to tax the GTX 660 Ti. Even at these settings, we're seeing an average frame-rate which doubles the requirement for most 3D displays - 259FPS is an embarrassment of riches for anyone looking for the smoothest response from their mouse.
It's a similar tale of excess for the likes of Diablo 3 and Call of Duty: Modern Warfare 3, which will no doubt both satisfy owners of 120Hz LCDs at these higher settings. The shadow settings in Diablo 3 are set to high, and smoothing is crucially enabled too - though removing this bumps for the frame-rate up by a further 40FPS at the cost of some very slight pixellation to these elements. In any case, the lead is considerable for the GTX 660 Ti, with over 50 per cent gains in performance over the HD 7850 - not bad for an extra £50. However, neither of the weaker cards fail in their plight to achieve 60FPS during our run-through of Old Tristram to the first waypoint.
"The gameplay matrix suggests a law of diminishing returns on less demanding games and with most displays maxing out at 60Hz, 1080p60 is a viable target even for today's 'entry-level' enthusiast graphics hardware."
|HD 6870||HD 7850||GTX 660 Ti|
|Call of Duty: Modern Warfare 3||117.5||127.9||158.3|
|Saints Row: The Third||34.8||40.6||54.0|
DiRT 3 is another sterling performer at ultra settings, during which we drive a Cross Rally lap with seven other AI cars to the tune of 74FPS on the HD 6870, and 122FPS on GTX 660. The frame-rate improves gradually as we overtake more cars to take pole position, but the average is more than palatable from the starting line, for those keen to v-sync to a 60Hz monitor. Rage also hits this level of performance, though this isn't necessarily a ground-breaking achievement given how thoroughly id Software has optimised the game since launch. Unfortunately, we can't break free from the shackles of its 60FPS lock, even with v-sync disabled, to show the extent of any one card's lead over another.
Moving over into RTS territory, we find StarCraft 2 to be stutter-free on NVIDIA's latest card, even with shader and lighting settings at ultra. This is enough to service a 60FPS game while v-synced, but the HD 6870 and HD 7850 suffer from micro-stutters when new structures, such a pylons, are planted in quick succession. This ruins the flow of play in our 4v4 replay game on Kula's Ravine - to such a degree that it makes the controls less dependable during any climatic stand-offs. Lowering these settings to the next rung down becomes a necessity for competitive play.
The only game which doesn't quite make it onto the 60FPS boat when using the GTX 660 Ti is Saint's Row: The Third. This is yet another title that takes advantage of DirectX 11's feature-set, where playing through the introductory bank heist level leaves us an average of 5FPS shy of our target. The other cards struggle to greater lengths, inevitably, but frame-rates improve from running with DX9 quality lighting and shadows.
NVIDIA GeForce GTX 660 Ti: The Digital Foundry Verdict
"The GTX 660 Ti is an excellent GPU with strong performance, but this time around, it's not quite the breakthrough product we were hoping for."
It's clear that the GeForce GTX 660 Ti is a highly capable entry in the Kepler line-up, even taking into account the nips and tucks its specifications have taken compared to its elder siblings. Evidently, having both the memory bandwidth and ROPs massaged down to permit a lower price has done little harm to its ability to run games like Battlefield 3 and Crysis 2 at 1080p60. Bargaining for uniformly maxed out graphical settings may be off the cards here, as we've seen, but gameplay can be quickly put to rights again with a few light tweaks to the visual settings.
On paper, the Power Edition designed by MSI offers a sensibly weighted balance between the card's heat and decibel output, and the nature of its factory overclock which elevates the boosted core frequency to almost that of the GTX 680's 1110MHz. Given that the card is priced at £249 - similar to many of the conventional versions available - the value proposition begins to skew in its favour when considering performance-per-pound. Up against the enthusiasts' sub-£200 favourite, the Radeon HD 7850, it's clear that there's a considerable amount of extra performance that does warrant the premium - though reports like Anandtech's suggest that at this price-point, both AMD and NVIDIA cards have their charms.
In review, the performance of the GTX 660 Ti - cutbacks and all - does feel proportionate to the announced £250 price point. Our only concern is that prices are beginning to creep down on the GTX 670, to the point where certain models are available at £280. Commited PC enthusiasts may prefer to lay out the extra cash to get the full-fat ROP count and uncompromised memory bus, or else wait for pricing on the GTX 660 Ti to open up a wider gap to the higher-end model.