Great question. I honestly don’t know the answer, but I too wear an 11.5 shoe and these fit just fine. Rule of thumb is that you want some room because of bigger socks and our feet swelling during the day and in altitude. Read some reviews and see what you can learn, but as I recall, they fit like a true 11.5.
If you learn that these work for you, I’ll gladly sell them for $400 but you’d have to cover the shipping. Let me know what you find out.