As has been said by others, I too like the 3" in smaller ships withthe shorter horns. It is important to use the comparable horns with bellcranks according to size.
On the "big" planes, a 4" BC is about mandatory. I just don't think a 60 plus oz. plane with a comparable size engine would fly as precisely using a 3" BC. The whole set up benefits from the leverage and ratios.
Interesting that Tom Morris sells 3 1/2" BCs.
I have found them to work quite nice in the 'tweener" size planes. Like the 56" Skylark which was originally .35-.40 powered, but often gets a .46 now!
Bill <><