Dean,
The GMS you have is not that bad of an engine. Put a 9x6 on it and try it that way. Let it unload a bit. I have seen those turn 9x6 props well over 15K rpm.
The Jett 50 will turn up over 17K rpm using a standard APC 9x8 or 9x9. (you will not see it turn a standard 9x9 at 18K) You would not be disappinted with the speed.
For all-out Q-500 "sport flying" the SJ-50 is available with the SS muffler, tuned to run up in the 19K rpm range, utilizing the APC D series pylon props (8.75x9W, 8.8x8.5, 8.8x9.25). This is actually a pretty popular combination lately, but is only useful on aircraft that can actually fly at much higher speeds. For a Patriot or such, the regular muffler and lower RPM band is more appropriate.
Speed with that q-500 set up is compairable to a full blown AMA 428 racing setup, just a bit more user-friendly. (140 mph plus)
However, as othere have noted, if you are looking for some intermediate speed to gather some flight experience, you may want to try something along the lines of a Thunder Tiger .40 or .46 pro. Utilize a common APC 9x6, and the stock muffler. This combination easily exceeds 110 mph, and is the same as used for many regional 424 Q-500 racing events. Break it in properly (as a racing engine) and don't abuse it, and you will have pleanty of speed. The TT-40 and 9x6 will easily turn over 16K rpm. A TT46 will do even better. If you want some more speed from the same engine, install a jett-stream or ultra-thrust muffler, and the engine will respond quite nicely
These engines are actually very well made products, and a good value.
Bob