Dealers were given 11% last year on S3's, but they seem to be meeting their targets so 10% is a good deal if you can find one that is made, or a dealer has on order to be built, hence you have to decide if it has the right options, some S3's may have been sitting on Dealers forecourts for up to 6 months, Expect 12% on those, and they are the best deals for sure. The least deal you will get is when you order one to your spec, and it will take 3 months at least to your door.
It took me ages to find one with the best options package I wanted with out having options I did not want or pay for, and then It is not perfect, I wanted parking sensors, and could not get a car with those and all the other things I wanted, so I would list all the options you really want in an preference order and start searching.