The upper limits of safety on a bicycle frame---very heavily loaded with motors and batteries---in my opinion is in the 25-30 mph range.

Your brakes, suspension, tires, and frame itself are not really designed for the abuse of high speeds.

Also when you get to over 25 mph you are no longer safe to be riding bike trails for the other users.

With an Electric Motorcycle you will have a much more durable frame, heavier brakes tires wheels etc.

There is a guy that lives near me that is doing 30-35 on a cruiser bike with a gas motor---practically no brakes, no suspension. He is just asking for a dog or cat or kid or car to end up in front of him----ugly result.

The super lightweight advantage to low power useage on a bicycle with assist goes away when speeds break about 25mph.