It might help to get specific: I fly a Goldberg Eagle 2 with the OS 46AX. Yes, this is more power than the plane needs to fly well. BUT: The extra power is a plus on takeoffs as there is more than you need to be SURE you get off the ground safely even when your takeoff roll is not as neat as you'd like. Also, once I reach the altitude I want I throttle back and do not fly at over about half throttle (I just soloed last week and am not ready to fly faster in most cases).
As I learned from 25 years of riding motorcycles: It's better to have "too much power" and generally not use it than "too little" and then suddenly need it.

The 46AX is a great motor and as other have noted, will allow you plenty of growth with the trainer as well as the ability to move it to another plane later