I'll tell you this. Getting a very expensive cpu is a waste of money. Most of the time it just sits there idle and even when you're intensively using your pc (like gaming) Core 2 Duos stay around 5-10% cpu usage. The only way I've ever had my cpu usage over 50% is by running Super PI, and then it still only was the 8M test that reached that number.
Games performance depends about 90% on video card and memory capacity... Out of that I'd say at least 75% is the video card and 15% is the memory and maybe I'm now being generous on the memory. Our old family pc runs Call of Duty 2 and Splinter Cell: Double Agent just as well with my video card as my current system does (give or take a few frames). And that's P4 vs C2D, 1GB DDR-400 vs 2GB DDR2-800.
You'll only be needing anything higher than an E6600 (which in my opinion isn't necessary for the average user) if you're going to do some extreme number crunching that requires a lot of juice from your processor.