I always prefer a fixed factory HD cooling fan,....and GET a shroud, it makes a world of a difference, space the fan so that at least 50-75% of the blades are tucked inside it for a good suction effect, try to maintain 1" or more away from the radiator itself, as even fixed plades flex under extreme RPM, as well as driveline shift, which might cause the fan to chew into the radiator....