Both models occupy the no-man's-land between luxury cars, four-door sports cars and fast grand tourers, but each has its own philosophy in which to deliver the goods.
The Brits from Fifth Gear wanted to pit the two models against each other, but sadly couldn't find the most appropriate versions for the job at hand.
From the Porsche camp they chose a Panamera GTS, which is powered by a normally-aspirated 4.8-liter V8 that develops 440 hp and 520 Nm (384 lb ft) of torque.
From Mercedes-Benz they went for the CLS 63 AMG, which in UK-spec comes with rear-wheel drive only and is powered by a twin-turbocharged 5.5-liter V8 that develops 557 hp and 720 Nm (531 lb ft) of torque.
Which of the two models do you think would win in the hand of a... let's say amateur driver on a racing track? Watch the following video and find out!