Actually the diff balls you choose will have something to do with how your diff works and feels. Break-in is also important.
There are two primary grades of carbide diff balls, #25 and #10. The #10 balls are "rounder" and more uniform. Remember there are manufacturing tolerances in everything, including 3/32" carbide balls, so the #10 balls are better.
To begin with, it makes sense that if your diff balls are not round you diff will not be smooth.
You put 12 balls in the diff, and the carbide balls are the toughest thing in there, far tougher than the diff rings. If one of the balls is a bit larger than the rest, you are really only using one ball. That ball will wear the ring more than the others and ring wear will be quicker because you are doing all the work with just one ball. No matter how far the ring wears, you will still be only using one ball.
On the other hand, if one ball is smaller than the rest, you are only using 11 -- may as well leave the small one out. I certainly don't have the equipment to measure diff balls; even a typical micrometer won't be accurate enough.
Solution is make sure you buy #10 balls. X Factory #6500 diff balls are #10.