ati is dominating right now. I bought an HD3870 a while ago before the 48xx series came out. The ram and processor overclock like crazy, it runs hot but I just turned the fan up a bit. I knew when that card came out, that ATI's next card (the 48xx series) would be an nvidia killer.
Okay, so I took the numbers out of my head, not so sure about the temps... But I will look into it, and come back with what I find.
EDIT: Okay, in this thread the fan speed matter is discussed, and at least one person reported he had his fan at 35% and temps below 50! I don't know if this is in idle or load, but I know I've read similar stories in other threads. And all this also depends on your chassi and the airflow through it. The temperature/fan speed curve isn't linear, so I don't think you'd get 20 degrees at 70%. It would be awesome, though