the interesting point to make here is not that the model s is necessarily faster than the M5, but the difference in acceleration between the two. I remember reading about the high incidence of driver caused accidents with the Tesla Roadster when it came out. Electric engines generally have more linear acceleration than traditional engines. The torque is available immediately. This is different than traditional engines, where max torque is available at specific levels. People, not being used to the immediate power, would often panic/lose control and crash. You can see the affect on acceleration in this video, with the Model S taking off faster, and the M5 catching up at the end.