I originally bought the 35+5cm but found it didn't sit comfortably on me . Went back to purchase the 40+5cm and it is so perfect.
Very comfortable, doesn't pull the hairs at the back of your neck. The 5cm extension chain allows for either chocker or standard length to be achieved.
I have worn it many days in the few months that I have had it and so far no tarnish, no green marks on my neck.