i have mine set to 1100rpm, if it gets warmer than 50°C then it will start going up and reaches max fan speed at 65°C. that way, my temps dont get higher than 70°C
Might as well have the fans as slow as possible as long as they are cooling sufficiently
Currently the fan is doing 1108 rpm and cpu temp is 52°C, with safari, mail and Adium open. On my lap so isnt perfect air flow around the laptop