Yes, I measured from the middle of the ac joint, not from the corner of the acromion or the greater tubercle of the humerus (which is what is usually done when measuring for shirts and coats). Of course I'm doing the measurement myself, so I may be off by a bit, but I definitely have a very lean build.

In any event, the comfort issue hasn't been a big one for me. I'm more interested in wind resistance. I've been learning to ride with my forearms roughly parallel to the ground when I'm in the hoods, or else I'm in the drops, because I can feel a huge difference in the aerodynamics. And I see people spending a lot of money on aero bikes that have much more subtle changes in frontal profile than a 6 cm change in handlebar width would make. I've seen the stats for the difference it makes wearing tight cycling clothing, or shaving one's legs, and I know these aren't trivial changes at 20 mph. I'm assuming that narrower bars would give me a small but appreciable improvement in my ability to stay with the group at 20-22 mph.

Also, since I'm not sure I can get the Cannondale C3 compact bar in this size (though I've only briefly looked), does anyone have suggestions for a similar bar that I could get in a 38 cm size? What are the differences in the Cannondale C1 and C2 and C3 bars? Is it just weight?