RE: Tower Hobby .75 engine
I've never run the OS 25FX, but I did try the GMS 32 on a Bobcat 25... and the power on it is very good.
It compared very favorably to how much excess power I get using a GMS .76 on a Bobcat .50... this engine has gobs of extra power for that airframe.
The GMS .32 also seems to be the favored engine for the .25 sized racing plane set. If you check out their forums, you see that a lot of people favor this engine.