I just migrated from a C7 to a C8-pro - kudos to the staff at Hubitat for making it as easy as it can be.
I followed the steps in the documentation - including shutting down the old hub and taking it off the network before adding the new one. I also disabled my cloud based apps like Amazon Echo and Maker API. The built-in cloud backup for the migration made the migration even easier than backing up and restoring from a local source.
Once I updated the DHCP reservation so that it used the same IP address as the old one and enabling the cloud based apps I began to review my devices and apps to make sure all were still working - I quickly noticed the alert that my zigbee devices were using channel 20 and may experience issues, I expected this since I had read this was common after migration. My zigbee devices (bulbs, lightstrips, motion sensors, and inovelli fan controller) were not working. I changed the zigbee channel to 25 and waited until the next day to see if they would start coming back online - they did not. I spent about 3 hours re-pairing these devices, when readded they came back into hubitat as the same device as before (thank goodness). There were a few issues with some zigbee devices not getting reconnected until all the others were powered off, I assume this was due to some acting as a weak repeater.
After fixing the zigbee devices all has been working great, and I do notice an improvement in response and overall performace. I'm feel a bit better being on a new hub - when the C7 hit the 8 year mark I figured I had got my money worth ! 
