I drove the GTI VI a couple of weeks without ABT and now with ABT...the sound is phenomenal....I do not know who told you different.......
The pullingpower is .........well once you've experienced that ...you never drive a normal GTI in your life again.....mark my words..

(I drove the GTI V unchipped for 4 years).
The difference between 17 and 18 inch is with "looks" (and yes take the nicer alloys) a totally different ballgame and in my opinion only slightly more uncomfortable...

The RNS and camera gave me a lot of pain with malfunctions but after weeks of VW argueing it is now working again.....
Leather aftermarket proves to be quite better...
BTW I have nearly all the options....so feel free to ask.....
groetjes
Erik