well not all handlebars are measured outside to outside. My Ritchey is measured center to center.
Here's a thought. A narrower handlebar will make your steering a little bit more twitchy (smaller turning radius). And out of the saddle sprint and climbs, as you're pulling on the handle to sprint or climb fast, it would require you to keep a more stable balance. more wobbly another word.
A wider handlebar would give you a more neutral steering, albeit slower or less twitchy turn (larger turning radius). Out of the saddle sprint and climbing would give a little bit more stability. But too wide can make your arm fatigued, feeling too stretched.
All is taken into consideration of your bike characteristic (twitchy or more laid back handling) and of course, the all important, your shoulder width.
Hope that helps.