Hi I have an OS .61 on mine and the biggest problem I have is prop limitation. The motor will put out enough hp to go faster, but because of design I can only go so large on the prop.I am thinking of a higher pitch prop. I have a couple on order now. When I try them out I will let you know.I currently have a cut down 13x6 Right now it is just a guessing game. I also have a "how fast" that I just received so I will be able to make accurate test.

os: altitude here is 4600'