Awat, what is your definition of "unlimited vertical?" I am looking for the kind of power where you could drop to idle rpm's, fly straight up until stall then nail the throttle and watch it climb out with force and aggression. By this I mean the same kind of authority you might see watching a regular takeoff with a quick stunt type plane where it is at idle and stopped on the runway and then full throttle added (if you know what I mean). Does the 50sx give that kind of power? If so I may go with the smaller engines. I am just fishing for ideas and want a good representation of which engine gives what kind of performance in vertical flight. All I have read so far is that the OS70 and 46 size engines give vertical but slow and gradual. This to some could be considered "unlimited vertical." Although this is not what I want.