Right, I have downloaded Everest and tried that:
Under load - after 10 mins with Prime95 100% on all 4 cores:
CPU = 64C
Core 1 = 72C
Core 2 = 73C
Core 3 = 79C
Core 4 = 81C
Does it look like maybe the heatsink isn't fitted right? Why is there such a difference between the 4 core temps?