Look at the benchmarks with respect to the GPU first, as maximizing your FPS at that resolution will depend a lot more on the GPU that the CPU. If a single HD6970 or single GTX570 is not sufficient, then you're looking at multiple GPUs. A pair of HD6870s will easily beat the HD6970: http://www.anandtech.com/bench/Product/301?vs=292
and not cost too much more. If they do, then you'll need to lower the CPU to make budget. You can get a Core-i3 and plan on an upgrade, or go AMD with a 970BE (a 955BE may nor may not OC enough) on a 900-chipset board so you can upgrade to Bulldozer, although you may not need to.