I recommend using an infinitely variable fan set up.... much easier to live with, and lower average temps for no sound most of the time.
CV fan control is a beautiful thing, and if you can get your hands on a surplus supply of car cell phone chargers, making pure analog controllers for them is beyond trivial. The easiest ones to work with IMO are the MC34063 based units, I use them everywhere (including my inverter)... I leave them on the original boards and just modify the circuit there, but the part count external to the chip is very low and throwing things into just about any board layout would be a trivial process as well.