I would go with the highside of the reccomended engine size too. If you want a .60 size Trainer , put at least a .60 size engine on it. You'll need the extra power to get out of trouble or flying in the wind.

I helped a guy fly his .46 size Trainer the other day with an old webra .35 on it. It flew, but just barely. I pretty much had to fly it at full throttle all the time. There was absolutely no power to spare. I like to be able to cruise around at half throttle still leaving plenty of punch left when I want or need it.

Good luck.