to answer a couple of questions,
Audi A3's are 5x100
A4's and 6's are 5x112
only found this out because i was looking for a set of wheels from an S3/S4 only to be told they different!!
i just bought RS6's for my A4. 18" £409 plus £25 delivery
OEM Audi RS6's are 19" and will cost you around £2000 plus tyres from Audi!!!!!!!!!!!!!!!
Replicas might not be as good quality, but for the price i paid, when i need new tyres, i'll just order another set of wheels!!!!!!!!!!!!
Stu