10.3.1. We had a few off-site machines that were very slow to logon, in the range of 3-5 minutes from password entry to usable desktop. Without ZCM, logon time was 20 seconds.

The fix was to remove all policy and bundle assignments, create a closest server rule specifically for these machines that included only one ZCM server, and add the following reg key. Logon time is now 40 seconds. Not bad. YMMV