My 2 cents... I had a tower trainer arf.  Flew well on a GMS 47, but it broke down so I put a OS 40la on it... didnt fly so well.  Put a magnum 52 4 stroke on it,,, flew awesome.  Lost the plane from a bind drop on radio.  Got a Tower Trainer 60 and put an OS 91 on it, ooo so much better than the 40 size.