Welcome to the forum, you'll find the members on here are a friendly and helpful bunch :)
You certainly have had some lovely cars and the s5 looks cracking :)
Cheers
Steve
as for 18" over 19" i`m not sure maybe the road was too hard on 19" so they got swapped out, if it was me i would look to see loads of service paperwork on a car thats now at 150k