Depends on the bike geo – I’m about 5’6.5″ and have 800mm bars on my suppressor (35mm stem) but have 785mm bars on my hornet (60mm are) On a medium bird zero am 785mm bars are far too wide with a 55mm stem.
I run 720’s on my bikes because any more than that where I ride and I would be clipping trees. At the end of the day it’s whatever suits you AND where you ride……it’s a compromise.
I ride with 810mm bars, and I like the feel. It’s not a dick measuring thing, it just feels proportionate for me. I’m a smidge under six foot, but have wide shoulders for my height. When I got all stressy that my bars might be too wide I experimented by getting into a comfortable press-up position then measured the width between the outside edges of my hands. The result?