For example: when i overclocked my AMD 3000+ Venice from 1800 to 2600 mhz i got an 30% boost in games like HL2, COD, EQ2, etc, with an nvidia 6600GT.
Now i have an 7800 GS (480/1450) and thats literally 2-3 times faster.
So i think a fast processor will give u a nice boost.
Going to an FX...