I have same problem. My E8400 Q818... for 3,87 GHz want 1,4125 V, and he is stable on this settings...i try go to 4 GHz but at 1,45v he was unstable...I don't want go up with voltages... I think that 817,818... batches are worst then 815, 814...
here is SS, prime is runing +12H...what you mean about temp, volts...?