I've got a Bofeili with the same motor/battery as the optibike pioneer, and much like
@grench, I can go about 40km/h (25mph) with motor assistance before it cuts out at 41km/h. There is a workaround, you can adjust the speed sensor on the wheel to get some extra speed, but then your mileage (odometer) and actual speed will be off. I use an app called "ridewithGPS" and it works great. When I got my bike it didn't have a throttle, but had one added, not sure why as I've used it once.