I've been using an XPS420 here for a while, so can offer some feedback specific to that system.
First of all, you won't be able to do another build inside the XPS 420 case, as it's a btx design, so normal atx motherboards wont fit (at least not without major case surgery).
A Q6600 overclocked to 3Ghz would still be good enough for most games at the moment. The exception perhaps is BF3 on 64p servers, where you'll get occasional mid 30fps dips,but even on an i7 you can still expect to get mid 40fps dips on 64p servers at times.
As it's a Dell, the BIOS is locked, but you can still (fairly) easily do a 3Ghz overclock using a BSEL/tape mod on the CPU to force a FSB increase to 1333. The stock cooler on the system is a rather good one, so you'll not have any worries about cpu temp issues. Should be able to find plenty of info on that on other forums, but can provide links to the guides I used if required.
IIRC the system originally comes with 3GB RAM, so you'd want to upgrade that to at least 6GB, and install a 64bit OS if you're still on the default 32bit Vista. You can use your existing key to do a 64bit Vista install as long as you find a copy of the media that matches the version you have.
In terms of upgrading the graphics card, if the cooler is of a type that exhausts the heat inside the case then you might want to add a case exhaust fan, as the XPS420 doesn't have one, and only uses the PSU fan for that purpose. There are no mounting holes for a case fan, but you can easily attach a 92mm to the mesh at the back of the case using cable ties.
As you've already upgraded the PSU, that would leave you only needing to spend on RAM (although ddr2 can be pricey compared to ddr3), a graphics card, case fan, and some thermal paste for cpu after the tape mod, which should be a pretty cost effective upgrade all in.
#8965265, By Andee The Budget Gaming PC thread
Andee 854 posts
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