Two Sedans with more similarities, such as the body structure, market segment, ground shadow size, height, and maximum occupancy, than differences, like the powertrain, horsepower, starting price, and fuel economy. First of all, the 2016 BMW 5 Series has bigger and thirstier engine; the 2015 Audi A6 Diesel gets 6 more mpg. Also, the 2016 5 Series is priced $8,500 lower compared to the base MSRP of the 2015 A6 Diesel. Among similarities are the body structure, market segment, ground shadow size, height, and maximum occupancy.