This particular last is known to be rather narrow, from what I understand. The standard advice I've read is to size down 1/2 a size, but go up in width. I take a 9E (wide) in it, and the fit is very good. I also briefly had a pair of Kent Wang oxfords, which I think are a more "standard" last, and a 9.5 fit fairly well, so it sounds like that advice is certainly accurate, at least for me. I have a very flat foot though, with a low instep.
Thanks for taking the time to advise me.
@pediwear Does this help or change your sizing advice in any way?