I voted on the X2 4800+, because I expect you have money to burn, since you asked this question in the first place. In a not too distant future, games will be multi-threaded, and you'll benefit from a dualcore processor, then.
However, if you really have money to burn, and don't mind upgrading, I'd go with the FX-57 and an extreme cooling solution, and overclock it like hell. Since it has an unlocked multiplier, there's no hard thing about it. I'm not sure how high it goes, but it's at 14 now. Then, when games get multithreaded, get a dualcore processor and sell the FX, or re-use it. 😀