Sadly, I very much doubt you can get the features you are looking for to work in your budget.
As a starting point, the case and PSU you've chosen aren't any good. The case is old technology (Ac97/USB front panel. It should be HDAudio/USB3) making it unsuited to the newer motherboard. The PSU isn't 80plus certified and only has one pcie power connector for powering SLI graphics cards. The case is also too small for 10.7” GTX 660 card you selected
Personally I doubt any dual channel memory ivy-bridge systems work well with SLI/crossfire, so I'd abandon that plan as the quad memory channel SandyBridge-E systems would eat £600 out of your budget.
As a side observation. Looking at the technical specs of the CPU you selected, it only provides 25.6GB/s of main memory bandwidth to 8GB, and the graphics card has 2GB of GDDR5.
If the current next-gen rumours are to be believed, that value is less than half the memory bandwidth of the slower DDR3 setup used in the Durango(64GB/sec).
If you've read an NDA for the coming system's technical specs, then that value will either not bother at all, or it might concern you about your new PC's shelf life for gaming. Either needing a new GPU with at least 4GB of GDDR5, or needing a system based around socket LGA2011, rather than the socket 1155 setup.
#9324074, By Getting back into the PC building game