The Core 2 Duo starts out with the E6300, followed by the E6400, E6600, E6700 and then goes to the X6800, which includes a hefty price jump. I think you'll find the E6400 or E6600 to be in best price:performance ratio. The X line is the Extreme versions with extra cache and a hefty price jump. The Core 2's run pretty cool, and AMD isn't having heat issues. Unless you're looking for a custom cooling solution, then the stock cooling (I'm assuming you'll purchase the retail CPU's) that comes with retail CPUs will be fine. If you would intend to overclock, then you should consider something a little heftier. Same thing if you're looking for quiet.

If you're interested in quiet computing, you may want to check out a PSU by Seasonic. Their S12 and M12 (the M's are modular variants of the S-series) are quiet. I haven't had one, but from what I've gathered, these are pretty quiet.

If you're not playing FPS games, in general, games outside of that genre aren't the most graphically intense. The only two non-FPS games I can think of are Oblivion and Need For Speed: Carbon, but there are probably a few others that are actually graphically intense outside FPS games.

I do think some of the complaints about Oblivion are overrated, but that would depend on the settings that affect outdoor views more. I haven't played it, but I do think that some of the reviews don't actually play the games as much as bench them and call it good.