I don't run an electric fan, but the issue has been tossed around a lot on TheDieselStop forums for guys running the 7.3L PowerStroke. One of the guys there is a cooling system engineer and he says that the stock fan on a 7.3L draws 25 HP when the fan clutch is engaged. There's no way you can get an electric fan that will deliver as much air. Granted your engine doesn't need that much fan power, but it's still significant. I would go with the highest CFM you can get. They're probably rated with no resistance, but it's still a point for comparison.
