May depend on where you live and if you need to wear a sweater under the peacoat. During my time in NYC, I found that I needed a sweater just about every day during the cold months, and certainly every night. My recollection is that a typical daytime high would be in the 20s to 30s, and the night time lows typically in the teens to low 20s. For me, I needed a sweater with those temps.
If you plan to frequently wear a sweater under the coat, I think the 38 would be the best bet. That is assuming a true 39" chest.
The Authentic is sized the same as the issue coats, but I'm not sure about the other models. If you could get a p2p on them, and then read the section on sizing at the end of my article at the link in my signature line below, you would have a good idea of the sizing of the other models.
You are, IMHO, a motherfucking champ.