I don't see a need for it to be an ancient code per se (though the thought of ancient precedent is interesting to me. Rather, anyone who knows the Sith understand their nature and understands that they will turn on each other at the drop of a hat. To me, that does create tension. Vader cowers before his master, but knows that if he can gain Luke, the he can overthrow the Emperor while Vader controls him. I agree with what timdiggerm said. They both know what is in each other's hearts (though never made explicit in Ep III, in the novelization it is affirmed that Darth Plagus was indeed Palpatine's master that he murdered after obtaining his knowledge). They know that one will successfully stab the other in the back, though they don't know who will succeed. Meanwhile, they simultaneously are aware of the need to preserve Sith teachings, meaning they have to keep each other alive till they can find a suitable apprentice. To me it is tension and it is interesting.

It's a good thing we're not doing a collaborative PT edit, because I have a feeling it would be extremely hard to come to any sort of story consensus :)

Then again, if timdiggerm's suggestion of creating resources for all fans to use were to be followed, perhaps more people could successfully finish their own edits. Anyway, that's a topic for when we're done with ROTJ.