@Bell_End: I have a very similar pc. Same cabinet and GTX570. Went with an i5 2500k OC to 4.3 GHz since processor is rarely a limiting factor in games. I'm actually about to put an Asus Xonar DX sound card in mine so I can hook it up to my new 55'' LED TV and get surround sound whenever i want to play Steam games with a 360 controller.
EDIT: Forgot to mention that I also have a similar, if not the same, Noctua CPU cooler.