The record in my ER was held by a homeless woman who routinely had blood levels over 500mg/dl (0.5). She came in once with a level of 745mg/dl (0.7). Obtunded but arrousable and breathing on her own.
We had a few career drinkers that would walk (by walk, of course I mean stumble, but they were able to get from point A to point B) in with .45-.55's. The highest I can remember seeing myself was something in the neighborhood of .67. .745 .. damn.. she's a pro.