Just to confuse everyone Arizona is for men and women and that's the reason that the narrow medium is a woman's medium, because the medium wide is the man's width.
I also have dozens of Birkenstocks and a lot of their models are unisex. Also the proper fit of a Birkenstock is supposed to be just a little bit larger than your foot because your foot rides around in the cradle of the shoe, and that's most important in the length, otherwise your toes will keep bumping up against the end of the platform.
I know this because the first pair I bought I bought in my regular size they were just a little too short and after wearing them for a month or so I began to realize that when my foot pushed forward it would ride over the end and it was painful.
I wear a size 10 wide but I always get a 42 even though they listed as an 11 -11 1/2. I could never wear anything that long in a regular shoe but I would not go down to a 41 it would be too short.