The CPU usage spike was between 28% and 41%, and again at 61% through 69%.
My CPU is an AMD x64 Phenom II x4 975 (3.6ghz quad-core) and is NOT overclocked. My temp alarm is set at 62*C, which is AMD's recommendation. I'm using a Corsair A50 heatsink/fan.
I've never had my temperature alarm go off until now, even when playing the D3 Beta for 4-6 hours at a time.