2fun,

A 91 2 stroke in the plane will be way overkill. The size prop you will need may even be a problem with the ground clearance not to mention things like airframe vibrations, firewall reinforcement, weight, wing loading, etc...

If you do the 61 then you will have a good match with nore than enough power

What prop are you using on the 46? To little prop or too much prop can also be your issue