There are a lot of different ways one can set up his z rods on an I3 style printer, only few are feasible for fast printing though, before installing the z rods one needs to make absolutely sure they are dead straight ( Roll on a flat surface ) If they are not theres pretty much no remedy, so exchange them for straight ones.
Stepper – Rod coupling:
Either get rigid couplings or stepper with inbuild TR Rods, reason is simple: we need to kill any play possible in the z rods to get the extrusions as evenly layered as possible.
Either get pretensioned nuts like shown in the picture or make sure theres absolutely no play in any direction. Upward play is bad as during fast printing there are numerous situations in which the extruder gets pushed up more than his own weight pushes down / the hotend tip melts in short timeframes. ( Extrusional force, crossing slightly overextruded print parts, step upward bending overhangs etc etc )
Top loose bearing:
As we are moving fast the top of the rod need an radial support, otherwise it starts to severely bounce around, a simple remedy are 8mm bore skate bearings ( 608 ) in an printed holder.