When you restore a backup from a C4 on a C5 no radio data (Z-Wave or ZigBee) is bought across.
For ZigBee you have to re-pair all devices - they do slot back in to their existing ID's though, so you don't have to redo any apps, rules, etc like you do with Z-Wave. But there's still some hassles around actually doing the re-pairing, especially configuration. I mentioned some of mine over at Anyone have a C5 they aren't using?
That's why it's currently quite appealing for C4 users to be able to move their Nortek stick over to a C5 as it means both Z-Wave & ZigBee devices from that stick carry across. It's literally as simple as moving the stick and restoring the backup as the OP mentioned.