As a reminder of what we are talking about (the only test I could find quickly):

http://www.autobild.de/artikel/mercedes-amg-gt-s-porsche-911-turbo-vergleich-5693390.html

They are comparing the AMG GTS and the regular turbo (with 520hp). NBR lap times of the turbo are about 11s quicker. Their summary states:

"Der 911 Turbo ist in allen Belangen schneller. Und deklassiert den AMG."

"The 911 turbo is faster in all regards. It declassifies the AMG."

And now, Mercedes found the solution to all their problems. At least with this "prototype" car they sent to the press Smiley