Well ive flown a 15x4...great thrust but to slow and had to keep the throttle up for speed - killer on fuel. Have the 14x8...flies nice but fast on landing(landing at my field is like landing on an aircraft carrier. If you can land here...you can land anywhere) I will try the 15x6 prop. Hopefully that will be in the middle. Hve to figure out if my Tru-turn wide spinner will fit on the 15x6. Oh well. Yet another trip to the LHS.