Its not too loud,expecially compared to my GPU fan when it hits 50% (xfx 9800gt) not that gets loud. I tend to think somthing is lying to me and not really running full speed. When it was running at 4800rpm that was getting noisy, but i might would like it at about 4000 =). my temps range from 29 idle (27 room temp) to 50c prime load.
Your temps are normal under idle and load. If noise is not an issue and you want the lowest cpu temps then run it full speed. I would find a sweet spot temps/noise level and keep it there.