I'll make some photo comparison pictures later today or on Friday if I have the time. I have no clue about cup size so the only thing I can give is my chest circumference and the comparison.
If I remember correct I'm about 83 cm around the chest. (nipple area I suppose)
I got the Air M Velcro short binder in size S. Sizing chart states 71~83cm for size S. I pull the velcro all the way to the edge and I suppose I could pull it over if I would try. Comfort level so far (I've been wearing it for almost an hour), super comfortable when it's just on, get's a bit worse after a while but it's mostly below the chest area, maybe I should loosen it a bit..
Also got the Sports Pullover short binder in size M. Sizing chart stated that the S was good for up to 82. So I took the M (82~87). Extremely easy to get on, the fabric was too rough too pull it off over my head though so I had to take my pants off to pull it down..

Binder seems a tad bit too big (what I was afraid for), but therefor extremely comfortable (haven't worn it for more than an hour yet). Rearranging your chest it difficult because the sides are low cut so that needed some fiddling. Will imagine it being way too tight though if I'd chosen the S..