I run DA 9000 on my S-Works. When I first bought the bike it had S-Works cranks and rings on it. I changed to a DA crankset so I could put a power meter on it, I was pleasantly surprised to find that the shift quality had also improved (and I never thought there was anything wrong with it before). The point being, is that I firmly believe there is a difference, although perhaps slight, between the Shimano rings and others. They all shift, Shimano just does it better IMO.

This may be a moot point if shifting is being done by Di2 however, but with mechanical, the shift was just a little more snappier, more immediate, less hesitation etc.