Hi!
You must have missunderstood this rpm thing with engines!
A certain rpm is not what is important. And certainly not aiming for what the manufacturer says is the rpm where the engine deliver it's peak hp.
All our glow engines can be run at a wide rpm spectrum. Your OS .46 LA for instance can cope with props that load the engine from say ...8000-17000 rpm without hurting the engine in any way...as long as you set the highspeed needle right (a little rich).

But for most sport models a 11x5, 11x6 or 12x4 APC is the best prop for your OS.

Regards!
Jan K
Sweden