^ That's a big chance to take though.
The Athlon will perform better in multi-threaded games, but and any game that uses enough resources to max either processor is probably going to be GPU limited anyway...
edit: Looks like it's a tossup on which one performs better. The Athlon wins overall, though:
(edit: that's a 550 btw, but I wouldn't expect a 555 to be very different.)