C47

I have a dual core cpu, and i get three readings from nxsensor; processor,core A, core B
when overclocking should i consider the processor reading?
during encoding these are the results
(proc,core A, core B)
PC Wizard 2007 : 49,50,55
nextsensor : 40.49,55
coretemeter : --.56.48
#1 : notice that nxsensor, pc wizard readings for both cores are both reversed when compared to coretemeter
#2 : proc temp in pc wizard is higher than nxsensor (either way it is lower that both cores)
so what reading does the processor correspond to (the processor die?)....and what significance does it have if overclocking

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another issue is that when idle there is a 10C difference between the two core....can someone explain why this is the case