I have a 205mm wrist. I bought the sports band and with the large it fits with room to spare.
Yesterday, I went to the apple store and tried the Milanese and the Leather band on.
The Leather fit with plenty of room to spare.
The Milanese fit with a some room to spare. It wasn't too small.
Either the guide is very conservative or it really depends on how your wrist is made. Some are more round. Mine are flat (wide) and not very thick.