I have mine at 4.0 with 1.21V (bios set to 1.22) and using a AXP 140 with 1366 mounting kit. I have DDR 2000 and the voltage for the QPI is 1.4V and the ram itself is set to 1.64V. I idle at 40/42C and load at around 75-80C. I have 2 120mm fans blowing air inside my case on the side pannel (connected to a fan controller and set to lowest speed for silence). So, with almost no noise at all, im at 4.0 and temps are in check. My C0/C1 was only able to hit 4.0 at 1.35V and the heat was too much.