I've been looking at the AMD Phenom II X6, the 6 core CPUs. Far cheaper than Intel and good bang for buck. You can also avoid the absolute top of the range gfx and buy last year's model for a quarter of the price without compromising too much.
If you already have a screen, all the peripherals and a case and PSU, you shouldn't need to spend anywhere near 900quid to get a screaming system.
Jim