Have you seen DarthNorman's map?
I think it's the best one I've seen. Although I don't remember what happens when you jump in the carbonite pit thing.
Well, sure these maps are great and all, but JK2 has a multiplayer duel map, Carbon Chamber (something like that), and the bsp name is duel_carbon.
The map is great, so great I made a quick video while fidgeting around in it:
I hope you'll like it, keep in mind this is just a quick test, I've never captured any ingame video before let alone edited it.
P.S. I just realized that there are 3-4 almost exactly the same videos on YouTube that are displayed in the "Similar Video" suggestion column on the right of my video... with the same maps and models! Guess I'm not the only one who thought of doing this, one of those vids is pretty darn good.