My 4850X2 2GB is not too bad when it comes to coolin; it sits at 3% fan speed on idle with the temps at about 40C, and I've never had it go above 35% fan speed when testing the card. I think I'll still go for a different cooler, mind. Or just take the jump for watercooling 
I have heard that the 4870 version of mindi s a bit louder though. Makes sense with it being a lot more powerful.
Zalman sell some good little fans that can replace the fans on mine, and I've seen some awesome coolers by Arctic Cooling for the 4870 X2.
Good luck!
Chris.

I have heard that the 4870 version of mindi s a bit louder though. Makes sense with it being a lot more powerful.
Zalman sell some good little fans that can replace the fans on mine, and I've seen some awesome coolers by Arctic Cooling for the 4870 X2.
Good luck!
Chris.