BRUSHFIRE. Stuart summarized all the reasons very nicely. The INtruder with the ST 90 will be a rocket in comparison. The ST 90 weighs about the same as pattern 2 stroke 60s of the era when it was designed so weight is not an issue. It responds nicely to a tuned pipe of you want to go that way, but will have plenty of power (more than we had back in the days when the Brushfire was kitted - I think Steve flew his with an Enya 60X).
The Intruder flies well, too, but was designed almost 10 years before the Brushfire.
My 2 cents.
Will B.