Would you prefer slightly long handlebar for bikepacking?, TourDivide I'm about to cut my handlebar to 620mm or 640mm
I have 620mm handlebar with minivelo and I'm very much tailored to the size.
However, I've read wider handlebar is better for controlling..
Mike hall (below) seems to be riding with slightly over-sized handlebar to me.. I'm not sure though

edit - mike hall is the current record holder for tour divide.
The tour divide is a long event riding 10-20 hours a day for over two weeks.
Your biggest priority should be comfort, your bars should be set to a width that is most comfortable for you.  Any small amount of discomfort with the position after a 1 day ride will be much worse by 15 hours into day 3.
If you are fortunate enough that your body will tolerate and/or adapt to a wide range of positions, you should then think about how your bar width is going to interact with the rest of your kit.  For example some bar bag designs interfere with your brake levers if your bar is narrow.
And what about other accessories you may want bar space for (gps, power bank, tri bars, feed bags)?
Once you answered these questions you will have your answer.
And as is the nature with bike packing you may only find out what is going to work well for you after you've experimented in training.