Well, after performing what appeared to be a successful upgrade, things just went South from there.
The first sign was an inability for UI3 to load a list of the cameras (a useful "fail" message with a suggestion to reload). While attempting to troubleshoot that through multiple reboots, somewhere along the line the v5 database no longer showed no clips for any of my cameras. So, no web access, no clips anymore.
As suggested by many, I had not deleted any of the config or keys for v4, so I re-installed v4 but it failed to load correctly when run, erroring out. Since this is a dedicated
Blue Iris server, I eventually just reverted back to a Windows 10 restore point to a working v4 install and everything is fine again. Perhaps setting a restore point should be strong suggestion for any Windows users performing this upgrade.
So I will not be in a hurry to upgrade to v5 until there is a really compelling reason to do so or I start seeing more success from other users.
Not a positive upgrade experience at all.