I typed up a recipe a while ago and I was able to find it 
The really important step is counting devices and "protecting" that number of Node IDs. I'll go over that part again...
When you start to add devices to your new C-7, the first NodeID will be #6. If you have 30 devices on your C-4, then you need to "protect" the first 36 nodeIDs in the C-7. On your C-4, look in Settings: ZWave Details and you will see all the existing nodeIDs in that first column, Node. You will, on the C-7 after restore, have all the same devices with the same NodeID but they won't be "real". You will need to go into each of those devices on the C-7 and alter the DNI. By doing so, you allow for your new devices to use NodeIDs that don't conflict anymore.
That's the first few entries in my hub. I have 32 ZWave devices on that hub today.. so I need to protect 32+6 NodeIDs: 38. I'm good, but 32 devices with NONE of them failing to Join first try?? hahahaha. So I'd look at protecting 40 NodeIDs just in case. For me, that means I have TWO devices I need to alter. Node 0x09 (009) and Node 0x28 (040). I won't 'step on' the next device 0x33 (051) until after I have a dozen ghosts. 
So... after restoring the C-4's backup to the new hub, altering the DNI of those two 'under 40' devices, I'm ready to start the actual migration process. I power down the old hub because it's about to become useless. All of it's devices are about to be ripped away.
I always Exclude devices from the new hub first. Always. This confirms 1) I have found the right 'dance' to get the device into Join mode. 2) that the hub and device can actually communicate. If I see the "unknown device excluded' message, I know I can Join the device with a very very limited opportunity for a ghost.
