I've hit over 50 MPH on my bicycle (no motor, just pedals). But, a good hill helps A LOT.

Most commercial E-Bikes will have some sort of governor that will kick out at 20 MPH (or maybe 30 MPH). You may be able to push it faster, but it will be on manual power.

However, those selling parts and kits may not play by the same rules. Likewise, bikes sold direct from China may not be regulated.

I see you can purchase a 5000W e-bike direct from China.

There is a huge crossover with parts between E-Bikes, E-Mopeds, E-Scooters, and E-Motorcycles. So, one may put E-Motorcycle parts onto a bicycle.

A lot of people relish the minimally regulated E-Bike market, but that may well change in the near future, especially if more speed bandits hit the streets, parks, and bike trails. And, if they start injuring themselves, or others.