I'm almost 6'3" and I have long, long arms (ape index?)....serious knuckle-dragger
My previous bike I ran 760mm for a while....and then 780mm with a 50-to-60mm stem. When I sold the bike I was really happy with 780mm.
Current bike came with 800mm bars and a 35mm stem(!)....but a lot more frame reach.
I rode it for a month or so....but my wrists were uncomfortable....particularly when climbing (?)
So I took 5mm off each end....and slid the grips in a few more mm. Total width now is about 790mm.
'Twas just enough to make it right (partly psychological too, methinks)
TL;DR: I think sweet spot is 785mm.