It has always been a belief of mine that a plane smaller the 80" wing span would have a wing load to high to fly good, But there have been a lot of good post with people flying 72" span planes with 26cc gas engines and say they fly fine. One thing is the lighter planes being made now can carry a little extra engine weight.

A engine from 20cc to 30cc will only be a few ozs different in weight, Unless it is some of the glow to gas conversions.

Milton