How do you lock pci-e timings

[Dj_]

I have been reading that if you dont lock pci/agp/pci-e timing then it can cause you probs. My default pci-e timing is 100 but since I o/ced my P4 560 to 4.15ghz (230x18) then the timings have gone up to 112. In the bios you can change the pci-e timings from 99-150, I tryed setting them at 100 but it wont boot unless the fsb is 200 and if I leave it on auto then it sets itself at 112. Any ideas
Im very new to the P4 scene, and havent ironed out my previous amd only experience.
Thanks