I used to wear the Linds Exxxtras in a size 11EE for a number of years (10?), the same size as my Rockports and New Balance shoes, sneakers, running shoes. Over the years I gained a little weight and my shoe size went to an 11 1/2. That is the size I got in 3G's Tour Ultras, about 2 years ago, when I went to replace my Linds. I have been able to use the 3G's without needing a wide version of them. I think they are made a little wider than a true medium, either that or the Kangaroo leather is much more flexible than cow leather.
I wear heavy winter socks in the 3Gs. When I wear thinner summer socks, they seem a little loose on me.