Two Convertibles with some similarities, but otherwise different in most aspects such as the starting price, horsepower, fuel economy, ground shadow size, height, and maximum occupancy. First of all, there is a $56,400 difference in the base MSRP. The 2018 BMW M6 has a higher starting price than the 2018 Alfa Romeo 4C Spider. Also, the 2018 M6 has a more powerful engine than the 2018 4C Spider, and it gets 12 fewer miles on a gallon of fuel. In addition, the 4C Spider is both significantly smaller and slightly shorter than the M6. And finally, you'll seat two more passengers in the BMW M6 than in the Alfa Romeo 4C Spider. Among similarities are the body structure and market segment.