Two Convertibles with more similarities, such as the body structure, market segment, ground shadow size, height, and maximum occupancy, than differences, like the modifications, starting price, horsepower, and fuel economy. First of all, there is a notable difference in the starting price of the 2016 BMW M6 Convertible, which is $62,309 less than the base MSRP of the 2016 Maserati GranTurismo Convertible MC Centennial. Also, a bigger engine usually means less mpg. But the 2016 M6 Convertible has a more powerful engine and it gets 1 more mpg than the 2016 GranTurismo Convertible MC Centennial. Among similarities are the body structure, market segment, ground shadow size, height, and maximum occupancy.