IMHO, I would go with the Saito 91. The money is worth it if you can afford it. For the weight/hp ratio, you can't argue. I used to run a OS50sx swinging a 12x4 zinger prop on it and it flew but no hover or vertical climb. Yea a two stroke has turn up speed, but a 4 stroke has the horse power to swing a big prop critical for 3D. I'm using an APC 15x4W prop. I can take off and roll about 10 feet and pull back and go straight vertical. Awsome power for the plane. The only time you want to throw the gas to this motor is ONLY in vertical climb. DON'T do it in horizontal or decline flight!