most pop cab selling was the 1.8T sales said it's quick off the mark and more buzzy then the 3.0, they never spoke about the 2.4 and very rarley saw one.
3.0Q is heavy not quick off the mark but once she is going lovely, nothing like the boxster, dif bread really, rear wheel drive mid engined toy, something to throw about espically the S model with esp(psm) off.
S4 cab is wicked, extra weight does slow it down but still rocket fast and sound the nuts!! The V8 purrs along.they don't make a bad S series!
Easy for me to say but it is up too you they don't make a bad cab.
Depending on age check out hood operation they did have probs at the start and the front catches needed changing and the sunvisors rattle, apart from that they are good, oh yeah when folding the roof back make sure it folds back ok section by rear windows as they catch sometimes damaging the hood lining so check these points out if buying used even if from a dealer.
Good luck anyway and we need to see pics once you get it