I have enjoyed reading the posts and there is some great information here! I just wanted to add a bit of information I have picked up while employed by an aftermarket fan outfit. The thinking was that a fan is functional in automotive applications, up to about 35 mph but after this point the "ram-air" effect took over and exceeded the fans cooling capacity. One of the advantages of electrical fans is that hard mounted fans take horsepower to turn. By using an electrical fan it has the ability to "cut off" above this mph sweet spot (when the ram-air effect takes over) and thus you get a little horsepower gain from it. The electrical fan in theory does not use quite as much horsepower when it is running and none at all when it shuts down. I believe that controling the fan thermostaticly is the best choice as engine temp will determine when this sweet spot is reached. Also it is my understanding that when you shut down a hot engine there is an effect called "heat-soak" the engine will heat up a bit due to the coolent not flowing and the fan being off. Many manufactures have included a circuit to help minimize this effect, where the electric fan will run a few minutes, after the car is turned off, if the temp warrents it. Any just my two cents worth, hope this helps!
Zardoz337