I took the car to Monza the other day. It is a very fast track, lots of straight and only a few chicanes, turns.
I was slower then the 992 GT3. Not on the straights, that was about the same, but I could not manage the corners as fast as them, except for the first tight chicane after the start. Bare in mind that my geometry was original and the others had done track alignments . My car definitely needs another geometry as my front tires have been worn with ''steps''.
GT4 RS does move around much more, on braking and in corners. Suspension has more rebond. It is a lively car, which adds drama and sensations. 270 km/h at the end of the straight. My son was doing doing 275 km/h with the 991.2 GT3. My brother with the F8 managed 300 km/h... but killed his brake pads 
There was a Cayenne Turbo GT. That thing is incredible. The F8 could hardly catch up with it on the straights . It was incredibly fast. Even through the corners, nearly flat trough. The guy used it the whole day, driving it to the max he could. No problems. We were stunned as we all expected overheating. What a machine ! I encourage any one into power SUV to try one.
On the way to Monza, I did the Saint Bernard pass and on the way back went through the Nufenen pass, and in-between did also some of the Centovalli with is a small road with hundreds of tight corners between rocks.
The GT4 RS is at home in these kind of settings. The king of mountain roads. It gives so much. The car is small and nimble, reacts instantly , engine is so alive , noise is crazy, you get so much more sensations then in the more planted and stable GT3/RS.
My son was driving the 991 GT3. Great to be able to do track days with the kid ! 
Next season they will release the big upgrade kit with new suspension ... I'm very interested in that one, because the GT4 RS is rather nervous out of the box (on the Nordschleife) it jumps around a lot... I think the GT3(RS) rides quite a bit more stable on the Ring.
