Majority of the config is in user.cfg
System.cfg contains a few important details such as network settings, cluster settings, license settings, device certificate, snmp settings and syslog servers related settings
When moving from one hardware family to another the general recommendation is:
1. First prepare the destination device with network settings, license, etc (network settings at the very least)
2. Then import the binary system config using the 3rd import option (screenshot and details are here -
https://docs.pulsesecure.net/WebHelp/Content/PCS/PCS_AdminGuide_8.2/Importing%20a%20Binary%20System.htm )
3. Then allow the box to finish restarting services (will happen automatically)
4. Then import the binary user.cfg (this may take longer than step # 2 and #3 as its importing a lot more than system.cfg) however should typically finish within a couple of minutes.
This is the high level. Please refer to the the doc mentioned by 'facusa' for a more detailed version