S70/2-swapped E39M "Grand Finale" with 627 horsepower! (Unfortunately, slower than standard M5 sibling on this track even with an equal setup. The interior was upgraded in order to be more competitive with the Mercedes-Benz E55 AMG Kompressor and to some degree, the first-gen Audi RS6 Plus.)
Even the peak trap speed of 292 km/h in this video is lower than the 302 km/h of the E55 AMG with supposedly less horsepower.