Those Talladega's came in either silver or gloss black. Those look grey, which would suggest they are either reps, or have been refurbed. If so, why?
As for handling, 17's give a better ride and handle a little more fluidly. 18's in my opinion, give the best compromise. The lower profile tyre gives better responce, but with less "give" has a slightly firmer ride. I've not driven a 6 with 19's, but I would expect the ride to be tiresome, so much so that you would not feel like pushing on and therefore never experience the addition grip they offer.
Cost of replacement tyres also has to be a consideration.
Much as I like the Vancouvers, they don't look right on a GTI. Almost as if someone has fitted the exhaust, diffuser and badges to dress up a GTD. If they are in good condition, you'll get good money for them if you decide to change them for 18" Monza Shadows.