I have been flying my US 41 for quite some time now on a GP Giant Stick. I am using a 40:1 mix with Stihl oil and a 20x8 Xoar prop. The US 41 has no trouble spinning that prop and is happily turning around 6800-6900 rpm. I have also used an 18x10 Pro Zinger and 20x10 Xoar. The engine runs great with either but the choice comes down to what you are happiest with on your particular airframe. Unfortunately, experimenting with these big props is rather expensive. Do yourself a favor, though, and buy good props. The better wood props don't cost much more than the cheap ones. I would stay away from the zingers in all forms. Haven't tried an APC but I haven't heard enough encouraging about them to make me want to. I have been warned to prop the engine to below 8000 rpm top end so that is why I avoid the smaller props.

Brian