A motor sized to be have a maximum speed of, say, 100 mph means by definition that the power the motor can send to the wheels at 100 mph exactly equals the powe

A motor sized to be have a maximum speed of, say, 100 mph means by definition that the power the motor can send to the wheels at 100 mph exactly equals the power lost to drag etc. by the vehicle at 100 mph (under the design conditions, presumedly dry flat road). Which means that the time to accelerate to 100 mph is infinite; and, more importantly, the time to accelerate from 70 mph to 80 mph is going to be ridiculously long. In other words, a vehicle that is power-limited to a "reasonable" speed is unsafe for normal highway driving because of insufficient acceleration to pass and avoid hazards. There's a reason that even a modern econobox can easily exceed reasonable speed. If you want to limit speed, you have to do it based on (wheel) rpm, not based on power.