A significant minority of pros are starting to use extremely narrow bars, like 38 cm bars. Trust me, if they could go faster, climb faster, time trial faster, etc, on wider bars, they wouldn't be trying narrower bars. Not only that but many pros are shying away from super wide bars. Lemond at times used extremely wide bars for his shoulders. Nowadays you don't see those 44s or 46s in use like that.

Although you may consider comfort, etc, for wider bars, the pros will regularly ride 5-7 hours. If it was that uncomfortable they'd use a different bar. It's not like they're paid to use a narrower bar, as long as it's the right brand (in most cases).

My shoulders are probably appropriate for 43-44 cm bars but even the batch of 42s I've bought/tried this year seem super wide. I prefer the old 41 cm bars that I've used for decades. I'll be trying 40 cm bars over the winter in preparation for 2014.

Having said all that I'll sometimes switch bars in the off season, for those long, steady, low-moderate effort rides. I'm not doing major efforts so I spend most of my time on the tops. For those rides I prefer a wider bar, like a 42. On our tandem I have 42s because sometimes you need that leverage. 44s felt a bit big so I stayed with 42s.