Markus,
Sport Auto tested two examples of Cayman S with PDK already and one example with manual gearbox. All other options were the same: LSD, PASM, SC and 19" wheels.
First example of Cayman S PDK Hockenheim time was 1.13,9min, second one achieved 1.14,2min on slightly different ambinet temperature.
Manual Cayman S achieved 1.14,3min on conditions that were almost the same as on first Cayman S PDK test.
According to Sport Auto on Hockenheim PDK version is from 0.2s-0.5s faster then manual depending on ambient conditions. We can assume that difference on Nordschleife is actually bigger(IMHO PDK is about 5s faster)...