Hello.
I was unable to find any way to control cooling system behavior on my 6750 XT Gigabyte OC using AMD Adrenalin. Manual fan curve doesn't work at all. Limiting max speed doesn't work.
Using presets like Quiet and Balanced does initially has some inpact on the speed but in the long run it will always max 3000rpm to maintain GPU at 65 degrees. I gather 65 is way low temp to max cooling system at that point.