My experience with White's has been that the Brannock measurement is quite useless as I had to size down a full size for my SDs and BHs. You might have also noticed that a lot of others sized down half to one full size in their boots. Your best bet is to get your tracings sent to White's or Baker's and have them give you a size. That way the fit is guaranteed. Also from what I have read, the Smoke Jumper last (4811) has the highest arch followed by the SD (55) last.