well, i HAD a kadet senior this season, and powered it with a webra .40 using a 10-6 prop. it had enough power to take off and fly around, but that was it. this plane was very overweight, b/c alot of spruce was used. (dont ask me why). if you build yours stock, the 40 may be sufficient, but i would opt to put the .60 in it. This plane likes to build tail heavy, so the extra weight up front would help. the 60 would probably be a rocket on this plane, but you have a throttle right?
If this is your first plane, then i would use the 40 to start with, then put the 60 on it later. another tip, take at least half the dihedral out, and add ailerons. it makes the plane more fun to fly and also help you from "outgrowing" the model, so you can keep it around as a backup plane, when you advance and buy a different model.