I have a RWD Dec 2013 S. On a rainy day, we held a Drive Electric Week event. Damp/wet roads. Flooring my car, there would be some stutter as the traction control figured out what to do. Went for a ride in my friend's early 2015 dual motor S same day, same weather. He floored it at the same spot I did; absolutely like the car was on rails, and/or on dry pavement. I was blown away.
I'm not worried (being in Victoria, not so much a problem anyway) with RWD, but I'm convinced AWD on Teslas is 100 times better.