I heard it was more like only one size (I'm 11 dude, but 12 gal). And even then it sometimes depends on the make of shoe.
Wow, 6'8"?? I'm 6'3" and will never complain about my height again. Even I have trouble with the XL stockings, I've been thinking of switching to garters, at least that way I don't have to get them all the way up and there might be less chance of ladders. Maybe that would work for you?