I have bars from 580mm to 720.

Basically you have to match the bar to the stem. Shorter stem for wider bars on the same bike.

For me, for actual MTBing, 666mm is the absolute lower limit for having a good time on a blue square trail.

720 pretty much always feels too wide for me.

690 is approximately my Goldielocks bar width.

I like backsweep in wide bars a lot too. 20° or so.