I have a base with 18s , the nissan salesman I bought it from said of the two he had in stock he preferred driving the base one as 18s were a "smoother ride".
Don't think it was a sales pitch as the gt was cheaper due to the mega high mileage it had.
I've only driven a gt once but did find the ride with 19s noticeably harder than mine .. but not sure how much better handling is with 19s as didn't give it much as I do mine in the bends - as the salesman was with me.
I have no issues with 18s maybe look a little small but I like the fact it is different to other ones I see.
Hope that helps ..