uhm, have you heard about the in-famous Athlon Black Edition?
I have a PhenomII 555BE, running as a 980, undervoltaged...
But i cant rise the "FSB" by more than 15% withouth problems. I know that the K10 and K10.5 dont have a real FSB, only basic clock what gets multiplyed to the CPU cores, to the northbridge and the L3 cache, and to the RAM too, by three different multiplyers. Athlon models dont have L3 though. But still, might worth a try to see how far that CPU can go and how it comes back in the in-game FPS.