Porsche was faster from 0-100 and 0-200 due to AWD. Also it had a clear advantage on the short track. I'm sure that 0-300 would not have the Porsche on the first place.
At "flexibility" M5 has very good numbers.
As a negative point for the Merc is its fuel tank with only 66L.
I read a lot of comments related to CLS 63... It has no chance against the M6 GC