I'm not a tranny pro, but as I understand it, common wisdom is that ATF+4 and most other newer formulations are formulated to offer less friction, and more slip because most people don't want to feel the shift in their new car AT's. They do, however resist heat a little better than the older fluids, and one would think they may last longer without breaking down. Type F is an older formulation that has been around a long time, and generally offers more friction; i.e.: less slip at the clutches during a shift. Many racers and performance minded guys like the Type F because of this.

We're talking about very small amounts of difference, however. Most would never know the difference.

FWIW: I run Type F in my manual valve-body 727, and it works just fine.