Buy this jacket!!!
I'm 6'3, 160-165 lbs (depends on the day). That's to say, I'm tall & thin with an athletic build (40inch chest, 31inch waist). I purchased this jacket in a large and medium to see which would best suit my 'tween size needs (in most brands I'm a medium, although I tend to stay away from Marmot and North Face altogether because of their blocky fit; most Patagonia & Arc'teryx mediums fit me pretty well). I purchase items for their intended use and fit, so I was looking for the BC to be form fitting, but with enough flex/give to accommodate high output activity use. The large was too big all around, with the way too spacious torso being the biggest issue. The large would have only worked, MAYBE, if I was planning to layer under it big-time (i.e., planning to wear another full-on jacket underneath). The medium, however, fit perfectly (plenty of length in the arms, nice tailored fit all-around) and looks great! My wife commented that it was one of the coolest pieces she's seen me in. Haven't gotten the chance to test its mettle in the field, but it is definitely a stylish, lightweight & warm jacket!