If you were and aero freak (I’m not) wouldn’t you want your aero basebars to be 40cm (for example) instead of 42cm since that would be 2cm less bar in the wind? Considering how little time is spent on them it seems that the 2cm (3/4") width difference would be negligible handling/comfort-wise.
Out of curiosity, how wide are bars like the HED, Oval and Blackwell integrated bars?