The mopar kit was put together for, supposedly, max cooling with minimal drag. It may also have been based on "the tooling we still have laying around."

The science of cooling is just that, science. It is actually possible to over cool an engine, which is why a three row radiator does not always out cool a two row - you are actually exchanging heat back into the unit at a certain point. This gets into delta t principle and I am sure there is a multitude of studies on the web if you have a few decades to kill.

In terms of a 5 vs 7 blade fan, issues like a well-fitting shroud, proper fan spacing within the shroud opening, properly functioning radiator, and an adequate water pump with the proper pulley spinning at the intended speed will make a much bigger difference than blade count.

My guess is that the 7 blade fan would show a nominal improvement over the 5 blade. You'd have to measure the surface area and pitch of the blades to figure that out. And then balance that against the added weight of the 2 extra blades to see if there is any real advantage. There are also 15" 5 blade fans, and 18" 5 blade fans.

Sounds like a question for Mopar Action. To the best of my knowledge Rick has never published a full blown write up on OE fans, there are a few mentions of factory clutch fans in the early 90s issues that I will have to thumb through now.