When I bought my SL3 S-Works the answer I got talking to support at Specialized was that S-Works uses "pitch" fibers in certain areas that increase stiffness. Also more time is spent making the frame because it has it has a more complex layup. This supposedly improves the ride quality as well. Since I don't buy a bike very often I decided to spend extra $1000 for the S-Works not knowing if there is really a perceivable difference in ride quality. I am happy with the bike and don't regret spending the extra money, but if I had it to do over I would have bought a used one because you can get it for half price.