ffs doing some research for you stevey..
the i7 has hyperthreading which games do not use, and having it there when you dont need it actually slows performance, so you want to go with an i5 if you're gaming.

ivy bridge can't be overclocked as much as sandy bridge, but ivy bridge is about 5% more powerful than sandy bridge at the same clock speed.

So i guess my advice wouldnt be much different than marks' advice; find the video card you want, and build everything else around it, and keep the information above in mind when picking a processor.
Do you plan on overclocking your processor? How are you going to keep your system cooled? Do you want a fancy case? etc etc