What frequency for PCI-e???

hi guys,

i've got the P5B Delux WiFi/AP mobo, e6600 @ 2.91Ghz, 4GB Patroit RAM and the BFG TECH 8800GTX OC2.

my PC isnt running as it should....i just want to know, at what Frequency should you put your PCI x16 bus speed for the GFX?? auto,100Mhz??? the cpu is performing really good, but the gfx are par, which it shouldn't be...

i read on another forum that the bfg 680i mobo automatically sets your GFX from 100Mhz to 125Mhz, that is if you plug in the 7900GTX or 8800GTX. can i up my freq. to 125Mhz without any probs instead of leaving it on auto???

your help and advice is much appreciated!!