I think your old ASP will work fine, especially if the plane is tail heavy with the .25. If you need 3oz of lead in the tail with the .25, you may still be a little tail heavy with the .40. The .40 is probably 5 or 6oz heaver than the .25, but the lead in the tail is likely much farther away from the CG than the engine.

Like you said, you can always throttle back if the .40 has more power than is needed.

Eric