I got my DFU 1605's down to 20 micron, and that was not easy.
Shimming the DFU nuts with alu foil was a chore, and getting the AC bearings fitted correctly, amongst other little bits n bobs.

I do now have max limits on rapid velocity of <3000mm/min with the DFU nuts being a bit tight, so it's a trade off.

If you want rapids higher than 3000mm/min on 1605's, I think your minimum limit is 40 micron.