What Dizzi said. I've seen folks buy those high end heat sink fans only to install them into a case with crap cooling you've got to get the heat out of your case. If not then installing a super turbine of a H/S fan is useless.

I also go for checking out how much thermo compound you have between the CPU and the heat sink.
Checking the rating and compatiblity of the CPU to the MB and PSU and all that good stuff.

Check your case cooling

Run a test that will hit both cores.

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