Well, it was a noticeable increase, I can't really say exactly how many mph extra I was getting at top end. It takes awhile to crank it up and get the RPMs that high to the very top end and I hardly ever let it wind up that long, only on long straights. I would say at least 5-8 mph faster. I can hit 50 mph on a good day but I usually just cruz between 30-40 mph, maybe hitting 45 on a long road. I'm using a 36 tooth rear sprocket.
Now that I think about it, I can get up to 40 mph pretty quickly, but to go from 40 to 50 mph takes a pretty long time holding it at wide open throttle.