We are running a GP Express and upgraded to 4.0r2, which can manage 5XT/XP running ScreenOS 4, however, we were not able to make the GPX actually push the new ScreenOS 4 to our 5XT/XP's that were/are running ScreenOS 3.0.3r1.4.
In addition, after manually upgrading a 5XT to ScreenOS 4, the communication link between the XT and the GPX is not functional (updates sit at 20% forever). The only way we can get the XT's back on the GPX is by completly clearing the XT (unset all), configuring the IP's, deleting the device from the GPX device list, then re-adding the XT to the GPX and setup all of the functions and features again.
We have a feeling that our failed communication problem is due to a specific advanced setting on our current configuration, but we are not sure what is the culprit (MIPs, VIPs, VPN, etc). as we were able to resume communication with the GPX on a lab 5XP that did not have any advanced features enabled.
Needless to say, becuase of these issues, we are only running ScreenOS 4 on a couple of test NS5XT's. We are hoping that GPX updates (I understand 4.0r3 is out) will address the ScreenOS push issue, as well as not forcing us to re-create every XT manually.
Enjoy!