I am from a major east coast American city (NY / DC / Philly / Boston). One thing I've noticed is that, while the average height in these areas is indeed lower due to the immigrants, the white / upper middle class population is exceptionally tall. I would say the average young man is around 5'11, maybe even 6'. Indeed, just last Friday I was out with 10 of my friends (10 guys, also some girls) and I was the only guy under 6' at 5'10.
When you walk around the wealthy residential neighborhoods or the financial district of this city, the average height is noticeably higher than the touristy areas (mostly American tourists but plenty of international people) or middle / working class neighborhoods. In the office building I work, which is full of investment banks, law firms, software companies etc, I feel short at 5'10, even with a half inch wedge in my heel.
At my major east coast university, I noticed that most of the kids from wealthy suburbs of the major east coast cities tended to be higher. Often times, I would wear timberland when going to parties to make up for my relative shortness, and I did notice I got more female attention when I wore them. I really do think 6' is about average for upper middle class white men nowadays.
Anyway, this is why I would like to get a good 6 cm adjustment, even at my average to slightly tall height, as a person can be tall for the population and even tall for their region and still be noticeably shorter than their peers.