I know there's at least one or two people on the Discord that have adopted it and I haven't heard anything from them about lag.
1 - Did you update your CUO? (Don't)
2 - Does the lag persist after multiple restarts?
3 - Lag is pretty generic, is there something in particular you're running into?
TazUO is a fork of ClassicUO but they have features that are considered more "modern".
I don't know about Orion at all, but it may be worth noting that we've had some people in the past who needed to delete the folder %ProgramData%\Ultima Adventures
The Save file(s) are from the public UA server, so you may see other players/homes with items like that, but like Spectre said, all of the "modern" items are from that specific dungeon.
As far as I know, UA doesn't have a changelog other than the Discord server's Announcements. You are probably talking about Classic Assist's changelog.
I believe you're looking for "RandomEncounters.xml". I haven't messed with it myself but it looks to be fairly detailed. There's also a...