I guess a LOT depends on the camera.
When I used the 40D, it would get relatively warm, and start showing reds and dots everywhere. I had my 5DMkII operating at 28° CMOS the other night, but that peaked at 38°!!! I was alarmed at that! Looking at the pictures though, not much shows... guess Canon's new internal noise reducer works well.
Anyway, made a peltier cooled box
Will see how it goes.