Hello there. I just finished my Widebody 40 with a Saito.72. I had the engine on a GP Ultimate and a FunFly before, I used an APC 13x6 on those planes. The engine has a lot of thrust and very good braking with that prop.
I'm using an APC 12x8 on the Widebody, the plane is a little faster, brakes less on the down line but it seems a lot smoother and cleaner in flight. It still pulls it out of sight.

I would suggest the 12x8 for pattern-style. I didn't try the 13x6 but I guess from the experience with my fun-fly that it would be great for freestyle/3D. The 14x5 suggested above would be even better for slow flight, and expect a much more responsive throttle!

It is a very nice plane, I will try it next weekend with a LOT less control throw than suggested.

Good luck!