While no expert, I don't think it matters that much. Erring on the wide side is probably a better route to go. Between electric, classical and steel string acoustic guitars, you'll find so many different profiles and widths. Even going between electrics such as a Rickenbacker and a Godin, there is no comparison. Toss in bass guitars and game over. But most people adjust and get used to the instrument.
I have a very thick neck ukulele that I thought I would like playing that is now one of my favorites. And I even have a couple of 29mm 3 string instruments. The widest nut I have is 38.5mm.
What seems to be more important, at least to me, is string spacing. On one uke that had wide string spacing, I ended up bringing them in a touch. The amount if fretboard outside of the 1st and 4th really wasn't an issue.
John