Jett
Consider a Jett .90,1.0, or 1.20. They can rev, will be easier to install, and parts are just a phone call away. Jett will set you up with the optimum exhaust for your application to provide the proper powerband.
And if you really want to go fast, consider a different, less draggy air frame. The Dago Red from WM is a great plane.
RR