The FM1e is quite limited regarding the gearing... I replaced my chain and sprockets with smaller ones, from KP-designs (you can also check 2wheelhobbies.com for the "microdrive"), which are smoother and give it a bit longer gearing for more top speed.
Then the combo of spur and pinion: The largest pinion that can get in there, I think is 19T, if you keep it at 32DP (the big teeth) and the 79 or 80T spur.
As Wayne said, go for a lipo and see how much faster it goes.
And I also repeat: very well and very straight glued and very balanced tires!
Even if you put a 13.5T brushless motor, you can start doing wheelies, and this is not a good thing, believe me! First to go will be the rear wheel axle! So, you need to be very careful when opening the throttle!
The bike is easy to do wheelies, and its spectacular... but... damage-prone!
(Ask me how i know!
Finally, a 13.5T motor (around 3000-3100kv) will give you around 35-45mph... I have used an LRP motor on the FM1e, actually the one we raced at the RC Bike Worlds in 2010. That's VERY fast already and quite difficult to handle. Any faster than that you will need a very good hand/eye coordination, as well as a very well setup bike, straight in every dimension, new/clean bearings, nothing binding in the moving parts of the bike, straight-glued tires etc... Oh... and anything faster than 35-45mph... you definitely need a front brake as well...
With a 2S 4000/30C battery, you are looking at around 25+ minutes of duration with a 13.5T motor...
Since you fly, you know how to treat a lipo (don't over-discharge with a brushed system that doesnt have a lipo cut off)