Did you get your plate?
It's hard to tell. Since the wheel is bigger, the speedometer will read lower for the same speed. Downhill or with a tail wind the motor tops out at the same RPM as it did before but the bike will be going slightly faster. I don't think it makes a huge difference. Like equal to 1 or 2 teeth different on the rear sprocket.
The mileage indicated by the display will be less since the odometer will be off and the motor can draw a bit more current at top speed. I need to carry my GPS on the bike to see how much it affected the speed reading. I suppose I could also measure the circumference and compare it to the stock tire.
For street use, the high gearing works out OK. For off road, a larger rear sprocket would be good. Most of the streets around my area other than the freeway have a 35mph or less speed limit. I can easily keep up with cars on these streets, and they all speed.
I'll also say this thing is a real head-turner. When I'm passing by, people look at me with that WTF? look on their face. I think part of it is the noise it makes.