This is asked a lot, but no sticky about it. I posted a pretty detailed explanation of what happens to the CPU at high voltages, some suggested it be a sticky but it wasn't made into one. Anyway, the general rule is no more than 10% of you default voltage for any processor. For the NW P4s 1.7V actual (not what you set in the BIOS, but what your health monitor reads) should be your absolute max.