As you say as long as the temps are under control then you can set your fan where you want. I dont actually have Afterburner installed at the moment but im fairly sure you can set a fan profile yourself if you want to.
There really is no point in having the fan running any faster than it has to.
Just as a for instance Say you had the fan at 50% and it was a bit noisy and the temps were constant at oh lets say55%. Would i lower the fan down to 40% and run the card at say 63% ? Yes i certainly would.
However i beleive the cards run at about 80 anyway and thats pretty high already. Thats based on a His card and checking around yours is a XFX which seems to cope much better at around 65. If this is correct then i would certainly let it go up to 70-75 if it seems ok and the drop in noise level is worth it.