Your right, it depends on how you like to fly. I like aerobatics, vertical capability, pull out of maneuvers etc. I flew the same plane with an OS .61SF and it was ok but with the .91, I could do more things; sustained KE, great snaps, tumble, extended vertical etc. and enjoyed it even more! I would like to put a Saito 100 in one in the future.
As long as we are having fun flying our planes, I think that's important. The input on the forum gives others a chance to see what others have done and they can decide which direction they want to go. Happy flying.