The M5 concept isn't new to Americans. Stick a big V8 in a mid-sized car and beef up the chassis. Pontiac GTO, Plymouth Road Runner, The Bluesmobile...but the M5 is the full development of the concept. It's fast, roomy, comfortable, fun to drive, gets great gas mileage on the highway (25mpg +/- ), and gets lots of comments from strangers. People know what an M5 is and respect the car for what it is. I stopped at an out-of-town BMW dealer to buy a quart of oil and was asked by them to sell my M5 to them!
Passing power... you spend very little time in the oncoming lane. Safe and thrilling.
Better radio speakers. They are awful and aftermarket upgrades are $500 and up.