I tend to reserve the kick down "button" for lazy driving, as opposed to "active driving".
Kicking-down won't give you the "fastest" changes, which you would need for a quick overtake.
Pre-selecting the gear with the paddles is the "best" way to anticipate an overtake.
You can mash the throttle into the kickdown switch, but I find on the
S3 and RS3 this kicksdown into too low a gear, then its almost immediately in the red line, and has to change up.
Or if you push the throttle 100% but not activate the switch, the priority of the DSG box is to give you the smoothest change (not the fastest), so will "slip" the clutches, so sounds like the change is delayed. But if you watch the speedo, the speed will actually be increasing, it will just sound like its not going anywhere.
By far the best way is to pre-select the gear you want to overtake in, using the paddles or the stick.
Another tip for the "quickest changes":
To ensure a quick upshift - pull the RHS paddle WHIILST accelerating
To ensure a quick downshift - pull the LHS paddle WHILST decelerating, foot OFF the throttle.
This will give the "quickest" shifts.
If you try and downshift while accelerating, the DSG will have already preselected a higher gear, so will have to undo that to give you a lower gear.
From:
http://www.audi-sport.net/xf/threads/s3-manual-or-s-tronic.247746/
