M3ike:

I drove the 991.1 Cup and the 991.2 Cup extensively in Portimao this February. As benchmark we had Christian Engelhardt with us, multiple race winner in the German Carrera Cup, also winning 2 races this year. He drove consistently below 1.49min whereas the laps of Walther in the vids are around 1.55min. To gain another 5-7 seconds on a 4km lap I dont think so. And the Cup doesnt even have ABS, not a problem for a Pro, for me it made driving at the limit much harder especially as in the beginning we had too much front brake bias. Will drive again 3 full days there in December, also with the new AMG GTR GT4.

I believe your words and can only speak for the Nordschleife. Nonetheless, no matter where the above statement about the RS being faster than the Cup car originates from, the cars are surprisingly close in performance over one lap while they certainly make up time at different parts of the track.

On a side note, Lars Kern who drove the record lap on the Nordschleife, won the last VLN Race this year on a Manthey-Porsche together with F. Makowiecki.