You will pick up torque with the .52 four stroke and be able to use an 11 inch prop max. I think, as you suspect, the plane will have more initial pull but lose top end speed... but trainers don't need speed. I would go for it maybe with an 11x4 or 11x5 prop unless you want to keep some of your speed go with a 10x6. The other gain you get with this engine is a really cool sound