I've been trying to get a feel for how these would fit. I have 2 jackets of thinner material, kind of like track jackets, with 48" chests, and they fit me very slim (the excess just folds under my arms really). But for a slim suit jacket, I would take about a 42" chest jacket. I find the stiffness of the material plays a big role. I just ordered a Standen in a L, so im going to see how that fits, and pass some more judgement after that.
Im having trouble thinking about buying a new beaufort in a 38, then spending $100+ to send it to barbour and back to have the sleeves lengthened.