I'm building up a 2017 Roubaix Pro frame and my old bike had Easton Aero EC70 handlebars that were 44 center to center. I really liked the Easton bars; however, you can't use Di2 with internal routing with them.

For my new bike, I got some 3t Aeronova Team Stealth Handlebar that was size 44cm. When I mounted them on my new bike; I noticed that the center to center measurement was 42cm. The reach on the 3t Aeronova Team Stealth Handlebar is 104mm compared to 80mm on my old bike. I'm 6'4" 205ish lbs and wear a 44 suit coat. Would 2 cm make a difference in comfort vs the 44's I was using on my old bike. After you install the disc brakes it's a pretty big hassle changing handlebars.

Here are the new bars I got.
https://www.competitivecyclist.com/3...dlebar-ttt001k

Mostly it just depends on what you like. I put 42 cm's on when I built out my Paramount frame. Never really liked them But that is what most say I should have measuring to the bony bump in my shoulder. My Tarmac came with 42 cm's too. And I've since noticed that on longer rides, my wrist will bend inwards toward the frame when in the drops long. And that starts making my wrist's numb.

I've been saying for the last six or so months that I was going to go back to 38 cm bars I have on my Raleigh. I don't remember having any issues with my wrists and hands to the extent I have on my Paramount and Tarmac when on longer than 2 hour rides. Maybe I'll make getting the new bar's a New Years resolution.

With wider bars some say you have better control and your get better breathing. Going narrower is supposedly easier on your back and shoulder muscles, though I haven't noticed that difference.

So unless you have to have that money for another set if you don't like them, I'd just try them out for a thousand or so miles and see what you think.

Yes, it depends.
I'm 6'1". My first adult bike in 1984 had narrow bars. I prefer 36 -38cm ctc to this day. Not so easy to find.

I don't feel the difference in 2cm of width.