I'm 5'7'', 170 lbs wear a 40S suit jacket, and the M fits me really well. I said somewhere earlier that I probably couldn't wear a suit jacket under it, but I wouldn't want to with this coat. Probably my favorite thing I've purchased in the past 5 months.
I am 5'8" 160 lbs. I got the Bayswater in M and it was a bit big. I tried on the S in stores and it was a bit too tight so I returned it. I was at the factory store last night and picked up a S since it fit me perfectly. So I'd say there's a bit of difference in sizing. I couldn't tell you if there's a difference in quality or not, but I'm happy with the one I picked up from the factory store. Even more so since it only cost me $78.
Guys I know this thread is to compare the J Crew with the Schott, but does anyone have experience in comparison to an authentic USN Peacoat? I understand the 32oz wool from navyarmy surplus stores will be thicker and heavier. But what about the fit?