Two Sedans with more similarities, such as the body structure, market segment, starting price, and maximum occupancy, than differences, like the horsepower, fuel economy, ground shadow size, and height. First of all, the 2016 BMW M6 Gran Coupe has a more powerful engine and gets 4 mpg less than the 2015 Audi S8. And finally, the 2015 S8 is both slightly larger and taller than the 2016 M6 Gran Coupe. Among similarities are the body structure, market segment, starting price, and maximum occupancy.