I have installed and run- 
1) speedfan 
2) hwmonitor 
3) coretemp64 
4) cpu thermometer 
All 4 of these programs show the same temperatures on the 4 cores. 
i.e. 39, 37, 35, 33 
Aida64 extreme shows the cores being exactly 10 degrees less 
i.e. 29, 27, 25, 23 
Any ideas? 
EVGA 780i sli 
EVGA 8800gt 
Q6600 @ 2.4