When I do both GPU & CPU at the same time for longer than 40 mins, I get system shutdown because the PSU is getting overheated. Then I need to wait about 5 mins until the PSU cools down to be able to turn it ON again. I'm running out of ideas. If it's not RAM (passed MemTest86), GPU (FurMark can run for hours), CPU (Prime95 can run for hours) or PSU, why does it freeze then?
You just said it yourself, your PSU is overheating/you are tripping the overdraw protection. You need a higher wattage PSU to use your top of the line components. Don't keep pushing your PSU like that though, that's when catastrophic failure occurs.