Re: Capped at 350fsb.
If you got the CAS4 version of those HPC Reapers, then you should set them at 2.1v, and the timings to 4-4-4-15. This will make it more stable, by increasing the voltage and loosening the timings.
Disable the C1E Support function too, so the CPU speed doesn't throttle up or down.
Increase the vcore to 1.3375v, a more stability.
If that doesn't pass the 350FSB, then it must be that FSB hole that I've heard about. So try a different FSB speed, such as 370. I remember when I encountered this problem, for example....I couldn't get pass 375 on my P5N-E, so I skipped and went to 387, and it worked.
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