Hmm, I'll have to look into my numbers, just for the sake of sheer curiosity.

Even during the occasional days of playing for 6+ hours straight, I've never had my PC show any problems. No special/extra fans or cooling systems, just what the PC came with: on the graphics card, processor, and I think two in the case. Customary 'vent' holes on the side of the case, nothing on top.

Processor: AMD Phenom II X4 955
GPU: NVIDIA GeForce GTX 285

Game's on all max settings except no Multisampling, and not using some of the checkboxes (Ambient Occlusion, Depth of Field, Disable Cutscene Effects).