First of all, why the hell are they using the S63 Coupe in this comparison? You have the Panamera sedan and the M6 Grand Coupe both of which are 'four-door' coupes. The Mercedes-AMG vehicle that belongs here is the CLS63 considering the CLS started the fad. Why is the heavy S63 chosen? Probably because Autocar just doesn't care about quality and it is all they had available.
They decide to compare the performance by running the cars in the rain around some back road. They use a cell phone for timing which is done by the guy sitting the back seat. He is also drawing a picture while this is going on. Seriously? Not only is it raining you are using a manually timed cell phone operated by the passenger who is drawing?
The Panamera 'wins' if you want to call it a win. BoostAddict calls this garbage.