RE: Aircraft for an OS 91 4-stroke
Great Plane's Lancair. It is scale and aerobatic. It can fly slow or fast.
Mine currently has a 61 FX, but I have flown them with a Saito 91. The plane is smooth and goes where you point it. It will do all of the basic aerobatics and some of the harder stuff. The plane will hold knife edge at 4200 feet. The funnest thing to do with this plane is a slow roll the length of the runway 10 feet off the deck.
The secret is that this plane is easier to fly than it looks. It flies like a powered glider and is easy to see. The plane is cake to land, especially with the flaps. It is always a hit wherever it goes.