The max voltage AMD said the PhII can take is 1.55v, but I would try to stay around 1.45-1.5v just to be safe. Just increase voltage and HTT speed in small increments, test stability with OCCT, you can run a quick 30 min test for every few hundred mhz, then run OCCT for 2hrs when you found the max speed. Also, sometimes increasing the CPU-NB voltage will help, the safe range is 1.35-1.5v.