I keep mine at 35% on idle and it stays at about 60C-65C
For gaming I crank it up to 75% and it usually doesn't go above 80C. It's so loud that I can hear it from downstairs, but my headset really dampens the noise and I never hear it when gaming.
Which card do you own? Cards with the stock reference cooler or card with the stock dual fans? I've used both and my 4870 with dual stock fans runs 51-55c auto which is 29% very quite compared to stock reference but my 4870's in CF run about 60-61c When using the 4870 with reference cooler ran fan at 35% to get 52-55c which IMO wasn't that bad.