Two Sedans with some similarities, but otherwise different in most aspects such as the model year, horsepower, fuel economy, ground shadow size, and height. First of all, the 2016 M6 Gran Coupe has a more powerful engine and gets 3 mpg less than the 2014 S8. Also, not only S8 is slightly larger, but it's also taller than the M6 Gran Coupe. Among similarities are the body structure, market segment, starting price, and maximum occupancy.