Having ridden road bikes since age 12, I found the Ritchey bars on my mountain bike a little too wide for comfort, so I hacked a couple of cm off each end, remounted my perpendicular bar end extensions, and enjoyed the ride. I guess this adjustability is the one benefit of flat bars over drops.

On a road bike, I find I am very sensitive to forward reach, i.e., seat-to-handlebar distance, which is a function of top tube length, stem reach, and, to a lesser extent, bar shape.

For drop bars, a 38cm width works fine for me; 36 feels just a bit squirrelly/twitchy, and 40 just feels wrong. Interesting that the upper body is so sensitive to this dimension ... .