In this comparison Tiff is able to pilot the 997.1 GT3 to a laptime of 1:30.6 on the test track chosen for the comparison. The 991 Carrera S does it in 1:33.0 which is considerably slower. However, the GT3 does come with basically R-compound track tires so that does not exactly make this fair. If one is really trying to see which is faster around the track similar rubber should be used.
It would have also been interesting to see a straightline comparison between the two but we would expect the 997.1 GT3 to win that comparo. It would have also been nice to see the PDK Carrera S included to see how it how stacked up to both cars. Oh well, still a cool comparison.