I really apologize for the screenshots quality but the pictures of realtemp were taken during the realbench benchmark.
I was using HWmonitor to read the clock speed
I also tried downloading XTU but the enable/disable Turbo Boost button was greyed out https://image.noelshack.com/fichiers/2019/16/5/1555636554-2019-04-19-1.png
If speed is locked, could be Window's install, power plans or both. Was Windows a fresh install on the current hardware it's on? Not reset, a fresh install?
I had already turned turbo mode on and off and it seemed not really to have helped but now i get 4.1GHz during stress test with turbo on. Thanks a lot i can finally sleep with a clear conscience.
Sorry for the inconvenience ^^'