Well, I have driven both the RWD P85+, RWD 60 and the AWD 70D, 90D and P90DL. In Westchester County, NY, there are quite a few windy lanes with tall stone wall that remind me of many UK roads and lanes in the country... Is that the type of driving you will be doing or more freeway?
Also do you get any Snow or Ice where you are?
I think the more windy the roads and the the likelihood of ice and snow would dictate a dual motor S... The dual motor cars really do both pull and push in the bends and are confidence inspiring. On the freeway or highway, in fine weather then the rear engine car is just fine. I think you will need to allow your driving style and roads and weather dictate your decision. The S is a big automobile. I am going to be interested in your assessment after the test drives.