There still is the question of why it was unflyable. Was it controllable at partial throttle settings? Was it speed caused or too much throw on surfaces or balance. A too powerfull motor itself doesn't cause problems. Weight could have been an issue but then it goes back to a balance problem. The only way too much power causes a problem could be too much torque or too much speed. Too much torque would be mostly an effect on take off rolling to the left and throttling down would reduce that, too much speed would be causing flutter, flex in contol pushrods and failure of flight surfaces....

You still need to find out why you had problems.

The .25SF was a great motor, it's what the .32SX was made out of. It'll fly it well, unlimited vertical, probably yes with the right prop.

Any thick airfoil air plane needs to keep it's speed up when dead stick to land or you'll have a "dead" stick.... The thicker the wing, the more drag, the faster it slows down.