Well, I checked into the engine options......

ST 90 w/tuned pipe.....
Magnum .91 4-stroke
O.S 1.20 AX 2-stroke....... This engine runs well in the 9,000 RPMS range...... THat isn't enough speed according to my calculations......

I have never played with the speed game much untill I started looking at this plane.....

Really there are 2-major factors when trying to get speed out of a plane: Prop Pitch X and RPM's....

the .90 2strokes from jett can pull in the 15,000 rpm's on the ground with a pitch of 8....

Of course this will unload more in the air, but it gives you a starting point....

4-strokes sound great, but just don't put out the RPM's..... the compete with a HIgh power, high RPM engine.....
The valves on the 4-stroke would float way too much with high rpms and cause catastrohic faliure of the engine......
Now if someone were to take these valves and replace them with a TItanium valves and springs, this would lighten them up and you could turn more RPM's but not enough to pull the speed...

Justin