Any 20" diameter prop with 8" of pitch becomes horribly inefficient very quickly as forward speed increases. Propeller blades must be as thin and stiff as possible for best efficiency at these low blade angles. That is why there is such a large difference between thick wood props and thin composite props. If we were able to make use of 20"x14"s the differences between blade styles and materials are far less. A move in that direction will lower 3D performance and make our planes much quieter, and nobody wants that.