Maybe this will help. Before my current 550i, I had a 2005 Mercedes E55. It had 470 hp. It seemed that everyone on the road wanted to race me. It was really quite amazing. Porsches, Corvettes, Vipers, a Ford GT. The only race I lost was the Ford GT. I knew he'd blow me away. But it was fun. Mind you these were not long races. Just your common street stuff. The car had huge torque besides the horsepower. I jumped ahead of everyone because of the torque, which was 450 lb.
If you get a 550i and have Dinan install the re map mod (approx. $2,000) this car will be faster than that E55. More horsepower AND more torque. So if speed is what you're looking for, there it is.