I have a very frustrating problem: I can do prime stable 4000mhz on both small and large fft's and play games and benchmarks. The wierd thing is that i get random lockups and reboots that are not repeatable. On thing is for sure: it doesn't happen when idle or with 100% cpu load. One thing i know for sure is that it's FSB related since it starts to happen at anything higher than 423FSB on any multiplier.

I'm not sure if it's my P5Q or something else. I've tried everything I can think of: voltages, mem dividers and all the wierd settings in the BIOS.
I'm currently stable at 3807mhz (9x423mhz) with the followin settings.

1.16vcore (prime95, have to set 1.20v in bios with LLC disabled)
1.52vPLL
1.12vFSB
1.12vNB
1.98vDIMM (memtest86+ error free at 1060mhz so that's not a problem)

3800mhz is stable at very low voltages so it would be nice to see what this little E8400 is capable of.

I really hope that someone had and solved this problem. It's very frustrating to do stability testing with no prime95 errors, the bastard just freezes or reboots.