I also own a 2007 america, which on a good day will get to 170 kph, I run a 18..41 tooth combination which lowers the revs just a tad, there was no difference in top speed over a 18..42 tooth combination. I usually ride around 120 kph and dont feel the need for a 6th gear. A 19 tooth will certainly lower your revs quite a bit, but I I'm not sure it will make you go faster, possibly the opposite as the engine tries to pull the taller gearing, I could be wrong though and will be interested in finding out the outcome should you go to a 19t.
