Unfortunetly I've never run this stress test from Everest (although I just bought an Ultimate license finally) so I might give it a go! With that said I'm not exactly sure what the problem is but I don't think its instability to be honest. It sounds like some bit of software is loading up the CPU cycles (either Everest of something else)? From the graphs it doesn't look like your CPU is throttling and besides your CPU all the temps look pretty consistant? Of course this is just my opinion so take it with a grain of salt but I can't imagine system instability is causing your CPU load to randomally change like this?