It's not heat throttling. I notice that at idle the processor frequency is 3.692 Ghz, which is "turboboost" for this cpu. When I turn on Prime95, the processor frequency drops to 3.29 Ghz. When I stop it, the processor frequency rises to 3.692 Ghz. Shouldn't it stay high under full load? You can see that the temps are not excessive and there is no thermal throttling. And the CPU Total TDP doesn't go above 45 watts, when under full load it should be 80+ watts. Under Intel Extreme Tuning Utility CPU stress test, the frequency also drops to 3.46 Ghz and the watts range between 45 and 49, with the temperatures between 129 and 135 F. Here's a screen grab from Intel XTU of turning Prime95 off and on:
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