Why (excuse the fahrenheit) does Sandra report my CPU at 96.8, and MBM5
reports it at 123.

I'm inclined to believe Sandra, because MBM claims it's 105 case temp. It's
not any hotter in the house than it's ever been. (I keep it between 82 and
85f.

Before I changed motherboards the case temp never got over 98.

When I first got it back together, the BIOS reported it at 61c. I was
shocked and appalled. I pulled the heat sink and redid the thermal paste.