I was a 40 E and I wore a medium.. it was tight, and took me 17 minutes to get on, the first time (LOL), but, it bound great!
That was the 997 though.. not the tri top..
Something important to remember about underworks binders is if you get one that may seem too small at first when you try to get it on, it will probably actually fit.. it just requires a bit of wriggling around and struggling the first couple times.. lol.. but you WILL get into it.