Use a 5-blade fan and a OE thermo-controlled clutch fan, not a El Cheapo viscous controlled fan. A thermo-controlled clutch fan has a bi-metal spring in the front to sense air temperature coming through the radiator. When the air temperature ithrough the radiator reaches a per-determined temperature, the bi-metal spring locks the fan clutch and the fan becomes a solid fan. That is designed to occur at idle speeds on hot days (i.e: traffic lights). The fan free-wheels and does not rob horsepower at higher RPM when lack of air flow is not a problem. .
Use a 5-blade fan. A 7-blade fan acts as an air-dam and restricts air flow at highway speed. Five-blade varible-pitch fans work with a proper designed fan shroud. Some high-performance GM engines came equipped from the factory with varible pitch fans to prevent horsepower loss at high RPM.