ORIGINAL: ianwynne
If I may chime in. It's better to get an engine with too much power rather than too little, provided there isn't a weight penality.
I have an OS 50SX in my Hobbico Superstar trainer. My instructor has said on a couple of occasions, "it's got soooo much power".
To continue the upside of this statement is that your engine will only pull that trainer to a certain speed because of the design.
If you make your "second plane" a "stick" you will see a very noticiable increase in speed an perfromance from the same engine. That same engine if placed in a small spped plane like a Shrike will pull it well over 100mph.