I just maidened a U Can Do 60 today with a Magnum 91 FS. The engine's new so I'm still running it pretty rich and it still pulls this plane around just fine.

It's not a speed plane and GP has a Tech Bulletin out about not flying the plane full speed unless you're at a minimum 10 degree up angle. This plane is designed to be a slower flying 3D bird. The Saito 100 ought to give it all the pull and torque it needs while not overpowering it. I'd go with that one for this plane's design, along with a wide 4 pitch prop to give you more low end pull. Our Club President has this setup and he can do any maneuver he needs to with it.

BTW, you'll love this plane. It's the first one that I've maidened that I was able to grease the landing one the first try. It floats right in and sets down gently. I did put a brace on each side of the gear running to the fuse just behind the firewall to keep the gear from folding back on a tougher landing.