Jim, Crash,

...Only high RPM? Wrong!

Please read this about what can be done for an ST .90...

http://www.supertigre.com/engines/supg0235-man.html

...

In 3-D flying you NEED high power to pull out of a hover. If your tuned muffler allows the engine to have a good midrange too, DO USE ONE!
On the MVVS .49, for example, it is great!