Another option is to look at one of the many .32-.36 engines that are effectively a bored-out .25. While your average .25 will spit out 0.6-0.7HP, the .32-.36 ones are often 1HP or more.

If you do want to stick with a .25 though, the Thunder Tiger 25GP is a nice little plain-bearing motor that's reasonably powerful, quite light, extremely well-mannered and ultra-reliable (all good traits for 3D stuff).

I've not had a Magnum but another guy in our club does and, while it's reasonably peppy, it's not always "on song" whereas the TT engines are ultra-reliable. You might also want to compare the power-to-weight ratio of something like the TT25GP with oen of the ball-bearing equivalents. The 25GP is often superior because those BB engines can be quite heavy for only a minor increase in power.