Despite what the OS manual may say, an 11-5 is a huge load for an OS 40 LA (they also claim 1.0 BHP -- reality is ~0.78 BHP). It will turn at ~ 10,900 - 11,000 at sea level with that prop, but the torque peak is @ 12,700 rpm. An 11-4 will turn @~ 12,100 - 12-200 --- much closer to the torque peak. The 40 LA will spin a 9-7, or 10-5 right at 12,700 rpm -- perfect for max performance.