What is your protocol of stressing testing ?
Because we have no infos
And others infos
Like #1 said, could you provide more data? What voltages are you running, what is you stress-testing methodology?
If you have a proper cooler it should be right, but for temps you should test prime95 version 26.6 small fft torture test for at least 5 hours.
Also you should set the vcore manual start at 1.35and see if tou can get your system stable or not
Ur clock speed doesnt effect ur temp rly
Ur voltage do, so 4,2 and 5 ghz are same temp on 1,4 volt both
My 8600k is running on 4,5ghz with 1,15 volt
Ur should not go over 1,35 volt on this cpu if u want to use it longer than 2 years