It's probably very personal and depends on how, what, and where you ride.
I'm 5'7" and all of my XC and AM bikes have 25.25" handlebars and I'm happy with them. I could go a bit narrower, but not wider. I demo'd a friend's bike and it happened that his bike had wider handlebars (not sure how much wider), but I was so afraid of hitting trees with the bars, they were a major distraction.
On the other hand, I have 27.5" bars on my downhill bike and I'm fine with them. It's a totally different bike that I use only on liftserve trails that don't have handlebar-width trees that you have to thread your bike through.
Do you have any friends with wider bars you can borrow? That would be a good way to find out for sure.
By the way, how do you like your shorter stem?
I'm 5'7" and all of my XC and AM bikes have 25.25" handlebars and I'm happy with them. I could go a bit narrower, but not wider. I demo'd a friend's bike and it happened that his bike had wider handlebars (not sure how much wider), but I was so afraid of hitting trees with the bars, they were a major distraction.
On the other hand, I have 27.5" bars on my downhill bike and I'm fine with them. It's a totally different bike that I use only on liftserve trails that don't have handlebar-width trees that you have to thread your bike through.
Do you have any friends with wider bars you can borrow? That would be a good way to find out for sure.
By the way, how do you like your shorter stem?