AVX/2 creates a huge amount of heat in a cpu, it's like running a cpu at 130% under stress testing. Fortunately, almost no games use AVX, it's a very specified instruction set used in a few professional production apps. What that means is if temp testing you should use Prime95 v26.6 small fft as that gives a 100% load as close to identical as gaming usage as possible. It does not use AVX. Later versions than 26.6 do. For actual stress/stability testing, use Asus RealBench instead.
Because of the heat output created by AVX and a few other similar instruction sets, bios now contains an AVX offset. For everyday common usage this should be -2 or -3 (200 or 300MHz) which when the cpu detects AVX usage, automatically drops your cpu speed by the set amount. So if you had a 5.0GHz OC, and offset of -2, under AVX usage, the cpu would drop to 4.8GHz and a corresponding vcore voltage drop too. This can lead to instability in high OC, so most disable (0) the offset since all they do is game.