APC 11-4.5 is the biggest I'd go on this this engine. An 11-3 or 11-4 even better. For 3D I'd stay in the 11 inch diameter range to get max thrust and slow speed. 11-4.5 would work but it might not wind up fast enough and the top RPM might be a little low. These little engines like to rev.

11-3, 11-4, 11.5-4 is your range if you ask me.

Joe