After building an exceptionally heavy bo for someone at their request (imo too heavy) I realized a few things about using a bo which I can put into words which may help people picking out their own staff.
There is a sweet spot which is different for each person which has to do with their ideal staff they want for their purposes. The sweet spot is where when accelerating the staff you use ALL of your muscles and get the staff moving to its maximum speed for impact, and where you use ALL of your muscles to slow the staff down again to prepare for the next technique. This is also the optimal workout for you and your bo.
If the staff is too heavy, It would take too much distance and time to get up to speed to do any real damage, and would correspondingly be impossible to slow down. What this means is you are also not really engaging all of your muscles in a meaningful way to start and stop it. And it is innefective.
If the staff is too light, it accelerates too fast, and you are also not using all 100% of your muscles to do anything. And it feels unsatisfying and isn't massive enough to do any short range damage besides poking at someone real fast.
So I think there is a sweet spot which can be felt, which depends on four things. The length. The material, the taper and the width.
Length will add resistance. Weight will add resistance. Tapering will decrease resistance, And width increases resistance. And they need to be felt before finding the perfect bo for your purpose. Also Changing the length and the taper has a MUCH more dramatic effect on the handling characteristics then the weight and thickness.
I have cut off a half inch from either end from a staff of mine and it went from feeling sluggish to feeling perfectly balanced. So small changes can have a tremdous effect.