ePMP 3000 + 2000 + 1000 - fw + gps synchronization.

What about fw for epmp 1000 and 2000 (AP and SM) units It was previously recommended to stay with the older version of fw. Now can we go to 4.5 for all units? How about GPS synchronization. I have a mix of ePmp 1000 and 3000 units. How to set up synchronization correctly?