OK, here's the latest. I downloaded Motherboard Monitor (MBM 5) and ran it in conjunction with Everest. The 'system/mobo' and CPU temps were reversed. So I shut windows down and checked the BIOS settings and found out that the Everest readings ARE reversed. The CPU is what is overheating, NOT the mobo/system.
I've run the system with the sides off. It has a CPU fan as well as 2 80mm fans - one on the back/top of the case pulling hot air out, and one on the front/bottom pulling cooler air in, so I can't believe it's a case problem. Looks like it's time for a new CPU huh?