RE: What prop for a .91 OS 2S?
APC 11x10 or 12x10. You want less diameter and more pitch for speed. I love the 11x10 setup for my GP Little Toni. She is a very fast bird with that prop engine combo. Of course I am at 4600ft above sea level so you could probably turn a 12x10 the same way I turn a 11x10.