aspeed

As soon as a control line model record hits 200 mph, the AMA changes the line sizes to slow them down and presumably to make them safer. A high pitch prop may not rev up on the ground but will unload muuuch more in the air.  Combat planes always use a low pitch prop for good acceleration and so the motors don't overheat.  For speed high pitch is usually the way to go.  A square dia/pitch like 5-5 , 6-6, 8-8 etc. usually gives the best speed on a clean plane.