you try different pcie configurations? 100? 105? 110?

how about a bump to vich, although that shouldn't be necessary.

Can you try clearing the cmos. Running stock to see if it's gone. Disable the pci lock if it's enabled. Boot again. Then reenable it. Then try moving fsb up again?

I know my p5b had an issue with graphics getting stuck at x1 the first time I started o/cing. but a combination of vnb adjustment and forcing it to x1 and then unforcing it causes it to be x16 no matter what now.

edit: I know this is almost certainly incorrect, but have you tried a reinstallation? I don't know if I'd think it's necessarily a floating pci, since at around 360, if you didn't have a lock, you should have already lost sound and at 360 or so, start to lose sata as well.