I agree, they definitely are very similar cosmetically. This was why I originally went with the 550 M Sport. As far as gas mileage - yes, it is still not a Prius. The gas guzzler tax is a slight drawback. You have to consider a few things though - the car is more powerful with significantly more horsepower and torque than the E60 M5 - and BMW did manage to improve the fuel economy while accomplishing this. In the words of Richard Hammond - "there are jet aircraft that are more fuel efficient than the old M5." When BMW said it is 30% better than the outgoing E60, 30% of 10 mpg is only 3 mpg.
