I managed to capture a perf issue with getPermissionValue using LP 4.2.14

Any room for improvement?

Yes looks like there is. :)

What steps did you take to reproduce this? Is it something I'd be able to easily do on my own server locally?

1. Setup server with SpongeForge, Worldedit, GP, SF, LP
2. Equip wooden axe
3. Select 2 points (the more blocks between the better)
4. Execute command '//set water'
5. Execute command '//undo'

Repeat steps 4 and 5 to reproduce lag.