The answer to this question depends on number of facts. However, the bottom line is,
1000W Ebike can do as little as 22mph as top speed and as much as 45mph!
There are different types of 1000w systems. Such as direct drive motor, geared hub motor and mid-driver systems. They all have different characteristics. Direct drive system is designed for high speed. While geared hub system focusses on Moderate speed and more on torque. While mid-drive motors are engineered for very high torque. This means the bike will get to speeds of 15mph very fast but perform terribly on any high speeds.
The quality of the bike is very important, the total weight of the whole system plays a big role. If the bike is heavy and you have plenty of luggage and your total weight (including the clothes you are wearing). The top speed will be greatly reduced.
Let’s talk about Ersin Hybrid 1000 for example. This bike is designed for high speeds, the bike runs on 48v but the whole system provides 30Amps. It has a custom designed 1000w Direct drive motor meaning its heavily tuned for speed. This bike can reach speeds of 46mph or more without a sweat.
The things that affect the top speed of the bike is total weight on it, the road conditions (wet/Dry), (incline or flat), (tarmac/grass/sand/soil) and event if the battery is fully charged or not. The BSM chip inside the battery also needs to match the controller of the bike at 18amps or 25 amps or 30amps. The voltage of the system makes a huge difference too, especially on acceleration. This can vary from 48v to 72v.
As you can see, there are many variables that affect the bikes to speed. Best thing to do is find a good quality bike manufacturer with high ratings who already has done the hard work of working and testing all these variables and buy a quality bike parts, like with anything you get what you pay for. There may be many cheap alternatives on the market. But you don’t want to invest money into a system that is heavy and sluggish that is not reliable and may cause issues 3 months down the line. Also, you wouldn’t want the bike to run out of battery before it gets you to your destination.