The folks at CNCrouterParts have just released a new 5-start ACME nut.
I just upgraded my KRMx02 builds with the new 5-start ACME nut from CNCRouterParts. Its a much better nut.
The nut is interchangable with the Z-axis nut on the CNCRouterParts builds as well as the KRMx02 builds.

Installing the nut: