I found that thrust has a lot to do with knife edge loop. I had H9 Cap w/ OS 1.60. It does knife edge loop the best using 17x6 prop @ 10,000. When I use 17x8 @ 9300, it's not as good. So I'd maximize your thrust. Many people has good luck using 17x6 APC on Saito 180 swinging at about 9700 rpm. If you don't mind the aircraft's top speed being 54 mph, 17x6 would be your best bet.