Regarding performance, I run LB/Bigbox on an old Intel i5 3750k system. Its a little slow to load up, but after it loads its fine. Biggest annoyance is that in attract-mode, you can hear it working the hard drive (spindle not SSD) as it flips through the images and videos. Very disk IO intensive application. I'm finally upgrading it to a more modern PC, hopefully this weekend, and putting LB/BB on a NVME m.2 drive. So hopefully that'll quiet things down. I guess we'll see.
The metadata.xml file is a pig (429 mb on my install), so to optimize that you'd have to move to some sort of database, like SQL or something. And that adds all sorts of complexity, and will bring new problems. I understand why the developers haven't gone there. Would be nice to have the option though - "advanced users or large installs - use MySQL" (or something?). But, I'm making the assumption that that would improve things - no way to know until its tested.
Anyway.. back to the current beta.
I've been playing with the emulator management features in the new beta, and I'm getting lots of .NET crashes. (tried upgrading RetroArch) Not sure if its because I'm trying to manage an existing install or what. I might move/backup the existing emulators and let LB/BB take over and do a fresh retroarch install and see if that fixes things up. If / When I figure out the exact workflow that causes the LB crash, I'll post it up.