The 2019 Mercedes-Benz AMG GT 4-Door Coupe isn’t a coupe or even a sedan. It’s a hatchback or a fastback, and it’s one of the fastest, best-performing four-doors on the planet. The third car developed specifically for Mercedes’ AMG performance arm, the AMG GT 4-Door Coupe is a rival for the Porsche Panamera and BMW M5. It...