So it turns out that the Z-banding is caused in large part by the

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1

So it turns out that the Z-banding is caused in large part by the wrong distance between the threaded Z-screw and the linear bearing for the Z-rod. I made spacers that solves the problem (or at least greatly improves the situation).

Originally shared by Joseph Chiu

I updated the design for the linear bearing spacer so that the spacer itself is solidly mounted to the gantry. This upgrade greatly reduces the amount of drooping by the gantry.
http://www.thingiverse.com/thing:213752