57th-72th may be the "golden mile" but the pricey shops really start before and end after those parameters. Not that Coach is like Gucci, but I think there's a Coach all the way up in the mid-80's. Even the 40's are starting to get swanky, too.
It is a great block just to walk on and see the nice shops, buildings, etc. It is much nicer than 5th ave in my opinion. Also, a lot less crowded.