I went to the 9x3.8 APC because the motor was starting to get pretty warm and the instructions recommend stepping down one inch in prop size for 3S with this engine. Power is not a problem with 3S Lipo. It rockets out of a hover. I might give a 9x4.7 a try when I get a chance because it closer to the 9x5 that is recommended for this engine by the instructions.