Alas, I truly see no difference (except for minor RP moments).

They are evil. We kill evil! Let's gather and kill evils.

I've had a experimental character, fire giant that would go to Tribunal. I've no idea how much times did he die to maran just for being a fire giant. This is wrong - despite his evil nature, he was looking for order and peace. So, what is going on in CF:

Empire: elf? Elves must die! Goodie? Must die! Outlander?? Must die!!! Scion? Of course must die! Storm giant? Must die! Or take an oath, at least. We have power now - let's go take the orb. Or head. Or orb and head. And fetish. It's ours.

This is right situation for evil cabal, and I enjoy it.

Maran: fire giant? the drow? duergar? must die! Kill him, show him strength of the light! Show them light!

(Why do we kill? - To defend and to teach; How do we teach? - Through offering of blood oath).

So, practically it's two similar cabals with similar goals - to defeat opposite side. I liked marans lot more when they have been not in cabal, but loners (strong, respected and fearful). If you are making opposite cabal, this opposite cabal must have other ways to reach it's goal (victory of the light).