I haven't made a fan profile in a while, but when I was running reference coolers on my 5850s, man, I'd never ever let it hit 100%. Waaayyyy too loud. Even 80% was super loud.
I usually had it sit at 30% up to about 45C, then jump to 40% and ramp it up to 60% by 70C, then a sharp incline up to 80% at 80C, and stayed at 80 from there on out. I found a profile like that gave me the best performance/noise ratio as it only really got loud if I was really pushing it hard.