Bars can be measured center to center or outside to outside, so a 42cm c-c is not much different than a 44cm, measured o-o. Also, there are some bars that are up to 2cm narrower at the brake hoods, than they are at the ends, where the width is measured.

You should be riding whatever size you feel comfortable with. I ride 40cm c-c or 42cm o-o, but I've made the mistake of buying bars that were narrower at the brake hood (only 39cm) and that was my limit. I could feel that they were too narrow.