It is possible running 3dmark caused the graphics card to heat up. The fact that something in the case was running at 80c probably didn't help the graphics card much, which could heat up a lot(especially with crappy stock cooling), and heat the CPU up more pushing it to 100c.

I've been stable for 20 hours of prime on a single core amd, but until I upped the voltage one notch, it failed 7 minutes into fear. Games can be weird.