Me: 173lbs, 6'1", 32" waist, 40" chest.
The jacket is described above as "The Castelli Leggero Jacket begins with the Italian maker's stellar form-following fit. This is one jacket that won't flap in the wind." This is definitely not one of their race or aero fitting pieces, nor is it designed with shoulder curvature that mimics the shoulder dropped position on road/mtb. I purchased the Large and feel that a medium over my size Large castelli long-sleeve lightweight jersey may have been the way to go, BUT, my shoulders are pushing out the seems on the Large and the front is already nice and short. Not sure how this one got designed in such a fashion? At about 25 mph in a tuck it started flapping at the shoulders loudly, bit of a bummer to say the least. I like the pit "hole" and the vents on the back to I'm planning to take it to my tailor to have him "dart" the fronts of the shoulders (above the pectoral and near the pits) to help draw the shoulders forward for a better on the bike fit.
Super small, packable design is just what I was looking for.