I have a OS 91 on my Four Star and it flies it superbly. A friend flies his with a TT .91 while still another I know has a Saito 100 and they both fly as well as mine. I also own a Magnum .91 that I like allot. I just don't think you could go wrong with any of these. If you want to try something a bit overpowered and off the wall try the new Saito 125- same size and weight as a Saito 100