A shroud with the flappers would be the better option. When the air flow is low, it will still let the fan pull the air through the entire radiator, and at any point the air flow is higher, the flaps open so the fan can't block any air flow. The best of both worlds.

The OEM fan shroud on my 90 Dakota V6 5 speed had a belt driven fan and the shroud had the flappers. That one was the 1st OEM shroud with the flappers I'd ever seen (not that it was the 1st ever, but just the 1st I'd seen).