Sometimes my entire screen will turn green requiring a reboot. This has happened while gaming but also while watching videos in browser. I'm trying out undervolting/underclocking using LACTL. Have you experienced this? What was the cause and how did you fix it?
Could be worth a motherboard firmware update?
and i would double check all the power cables.
It looks ike mangohud is an application to monitor stuff.
I've never used it but you could give that a go - see if you're ever getting close to the 750W.