Somewhat different from what you are asking, but...we have an '11 MKX w/20" wheels. Have driven a '13 rental w/18" wheels twice, and both my wife and I think the 18s ride better than the 20s.
If you are young and don't mind a 'sport' ride, fine, but maybe you ought to try a SEL with the 18s just for comparison?
I am of the opinion that these SUVs need just a little more rubber between the road and the wheel to soften the ride.
Joe