Is it possible (now or in the future) to use MacFan to set a MAXIMUM fan speed?
This probably can be easily done; however, this puts this puts race2 into a territory of writing something that can actually damage an Apple computer. Even if he puts the standard "this program can damage or destroy your computer if used improperly and we will not be held responsible," he can be held liable for the damage.
For now, I'd recommend setting a min fan speed, but control the max speed using a tool like RMClock or CPUGenie combined with Rivatuner to underclock and undervolt. This will effectively reduce the temperature of your chips, dropping the fan speed.
Also keep in mind that your computer usually starts at a min fan speed with this computer and ramps up when it gets to hot. My iMac has not increased it's fan speed from my min settings, even with the CPU and GPU running at 100%.
Sorry johncol, I do not have any plans to add such a feature. If your fans are running too fast for your liking, it is possible a sensor is malfunctioning and causing them to run at full speed. I would recommend, in that case, seeking support from Apple.