for my ebike I used a 500W conversion kit from ali, and Im totally satisfied. However already looking to build something much more powerfull.. exploring the options.
for my bike assembly, I used this guide...
with my 500w bafang I can get 23 mph. But this is a stock, no tunning or boosting was made. But I've heard that people used to boost it somehow. It requires a more powerful controller and more voltage in the battery. Actually you can boost your motor as well.