Speed fan question........

I would use Core temp over cpu temp.

the CPU temp is the general, overall temp of your cpu, however the most important readings are your individual core temperatures.

You use the Core temp to determine the thermal limit, not the cpu temp

Also cpu temp is the temp measured on the mobo, whereas the core temp is measured by sensors inside it

I also wouldnt use speedfan for monitoring temps. If you use another utility, you mind find contradicting temperatures

I recommend using Everest, but for a free utility i recommend realtemp