My .91FX works best for me with a 14X6, on my old Cermark Sukhoi. The 13X8 works, but the idle is less reliable and the plane doesn't slow down very well. The 15X6 slows down almost too well, and the engine spools up a little slow. I like the 14X6 because it provides some braking, a reliable idle, and it spools up quick. Great combination.

Good luck,
Dave Olson