Fanch - I think your post is quite accurate. AWD has an advantage in putting the power down to the road in situations where the RWD car might spin its rear tires (standing start, exiting slow tight corners, and poor surface friction caused by rain, snow or gravel). AWD does not have an advantage otherwise. In fact, it does have disadvantages in all other circumstances (weight, smaller trunk, more power losses through the front drivetrain, and a less direct ability to throttle steer the car).

A C4S is ONE second faster around the 'Ring than a C2. Remember that a C4S has larger brakes and a lower, wider and stiffer suspension than a C2. Despite the fact that one second is totally insignificant on a track that long, the advantages for the C4S come from the brakes and suspension and possibly a better exit speed on some of the hairpins. I think your premise is correct that a C2S would be faster than a C4S, unless the track was wet (yes it does help at low speeds to get underway and pull out of slow corners, but not to prevent sliding at speed). I feel that when the weather is bad, I would rather take a different car from my Porsche and not compromise the purposefulness of my Porsche by adding the AWD. That's why I'm opting for the GT3...