My boots (which I have on right now) TTS, fit like a glove. With thick socks on, my toes come right to the end, but don't touch. If it were any smaller (Even a few milimeters) in width or length, they would be too small for thick socks. With thin dress socks they are too loose. With thick dress socks (wool blend gold toe) they are fine.
I bought the boat shoes for my dad, whose feet are identical to mine as far as I can tell, and I tried them on before giving them to him. There was maybe .25 inches in front of my big toe, but it was a little snug on the side of my pinky toe. (Also TTS, sockless) Tried them on again today (barefoot), after he has broken them in. They were looser, but I could still wear them without problems. (he wears them with athletic socks usually)
I have plans to get sort of a laceless boat shoe this spring to wear barefoot, and I might size down .5 for them, since they aren't laced and should stretch to fit. (I'm actually going to have a rawhide tie put on them, but non-functional, strictly ornamental. (Basically a boat shoe, but without the laces that go around the opening of the shoe, without the quarters/flaps that the laces lace through, and with no [or blind] eyelets. Think of it as a venetian on the boat shoe last, but with a rawhide lace bow/tie where a tassel would go.
Not sure if this helps at all in terms of langdon boot, but its the best that I can do.