I don't even care. I just drove the M5 and the responsiveness is incredible. I could only really experience 2nd gear because I didn't want to scare the sales lady pushing third. I can say after 30 years of driving and owning BMW's this is, at last, the finest driving fastest Beember ever.
Mine is due in July, I can't wait.
PS A slight change in temp, barometric pressure, altitude can add or subtract that difference.
nwood: that 400hp is at the flywheel. If you look elsewhere in this site you will find that several M5's were dyno tested at 340 to 347 HP. That's only about 15% loss to the rear wheels. I will say that's plenty of horses getting to the pavement....
lateral acceleration = 0.9G, transitional acceleration = 1.2G (the former you experience driving around a curve the latter you experience changing lanes ... but there are people on this board who REALLY understand this, unlike the pretenders like me!)