Most folks with hot rods prefer a stock clutch fan and good shroud instead of an electric fan. However, I think that is because the air flow of many add-on electric fans are over-stated by the manufacturer, and they don't work as well as the claims. You may gain a little HP with an electric fan under cruise conditions (no need for the fan to be on), and the engine seems to spin up a little faster when it does not need to move a fan, but you also need a strong alternator to keep up with the amp draw when the fan is on high.
I have a Ford truck with 5.4L engine and clutch fan, and a 2005 Mustang GT with a 4.6L engine and OEM electric fan, and I do not see any difference in the cooling system's ability to keep up with Texas heat. However, my electric fan is a Ford factory system that is designed to take the heat load. Many conversions use relatively cheap fans with shrouds that don't cover the radiator very well.