Clearly we aren't speaking the same language, or not understanding things correctly from either party. You cite there still being a 1 second gap which I just don't understand. Members on this forum are citing they are at, or near to getting their newer S6's breaking in to the high 10's. I have no recollection of anyone on this forum or the other forums running a second faster with high 9's in their RS7/6's. I do see many citing mid 10's for the newer C7 RS6/7's which is a half a second difference as I have it in my head.
As for the C5 S6's, there is no way a base line S6 is/was running 13.5 seconds. I have one. They are mid 14's - maybe lower when the planets align. Tuned, 'maybe eek out another 3/10's or even possibly a miraculous half a second faster max. A tuned C5 RS6 easily cracks 12's and is in high 11's with a few other odds and sods. This is what I have in my head as being a significant larger delta in the S to RS models than today's delta and prefaced my comments on the matter.