Shoot guys, I ran my IDI without a fan in Texas for a whole year (that would include summer!) and it did fine. If I had to sit more than a few minutes when it was fully up to temp, water temps would get hotter than I liked (225-230), but would fall back to 190* very fast once driving again. For a daily driver, E-fans would work just fine. Anything over 10mph and the truck was cooling (unloaded of course) to the point that I could drive at that speed all day and not overheat (190* water temp).
Powerstrokes ought to be more efficient when it comes to water temps, so you would probably have even better results than I did. I also picked up some fuel mileage as well.
In fact, during summer we had a day of pretty windy conditions (20mph), and to test the truck I parked it facing the wind. Water temp stayed at 190*. Ambient temps were 95-100*, fairly high humidity.
*Disclaimer* AC was inop, AC performance would have been very bad with no fan, and it would add more heat to the system.*