I too have a Sapphire 4870, and at first the idle temp was around 80, but with the new driver (8.10) I set the fan to 38%, and now it remains just under 50 Idle, and 60 stressed.
I have no problem playing COD4, Crysis Max settings etc.
I do have another problem. I would love to benchmark my machine with different CPU speeds, but my 3D mark 05 AND 06 will not run. It installs successfuly, but when I start the app, the opening screen just hangs, even if I leave it for 30 min. Not Responding. Before I load Catalyst 8.8 or 8.9, could it be my graphic drivers (8.10), or might the problem be somewhere else? Do other 8.10 users have isues with 3D Mark?