Hermes makes a good point about narrow bars and torso width. I'm on 40's because my shoulder width is very close to 40cm. On the hoods and drops, my arms are not tucked in or splayed out, they are lined up with the bars. I have no breathing issues. Enough people in the forum that have ridden in the field with me can tell you that the fit looks right. I would caution bigger riders going to narrower bars for some perceived advantage. It might not end up that way.