A friend of mine has 215 width tyres on his avus wheels. He says it gives more feel and he seems to prefer them.
also, bear in mind that low profile tyres on the 17's may look good on a mk3 golf or something, but the 17's are already fairly small on the S3, so fitting lower profile tyres may just make it look stupid.
s3 al, have you got a pic of the alloys please???