So, sorry for the other post, but I want update on how I managed to solve the situation. Basically I uninstalled MSI Afterburner and I downloaded Zotac Firestorm.
I selected 65c as targeting temperature, leaving all the other settings untouched and putting fan on auto (for some strange reason when I save my profile, this setting reverts back to manual, so I managed to set it on auto by editing the .cfg file).
I just played for one hour with Hitman, max setting, no frame cap, and...it worked.
The maximum temp I got was 66c, much better than 80c I had yesterday.
The only bad thing is everytime I start Win 10, I need to manually validate the message "This setting can make your GPU unstable" or something like that, and also granting access to the software on Win 10 (for some reasons MSI can pass the manual validation, but Firestorm can't?).