It isn't about temperature directly. Recent Intel CPUs instantly incur a noticeable penalty as soon as certain 256 bit or wider instructions are encountered. I

It isn't about temperature directly. Recent Intel CPUs instantly incur a noticeable penalty as soon as certain 256 bit or wider instructions are encountered. It doesn't matter if it's only a single instruction, you pay the penalty before anybody notices the temperature. After some fraction of a second it does revert to normal, if you haven't used any such instructions again.