I’ve been experimenting with trimming “I must obey my master!” while also incorporating Sir Ridley’s “Your mother once thought as you do” (albeit slowed-down). What prevented me from deleting “You don’t know the power of the Dark Side” was both Vader’s turn and making sure that Luke’s follow-up line made sense. The edit is a bit rough, but I’m sure Ady can do better working in the 5.1 mix.
Inspired by this I made a new version of the line. I slowed it down a bit and focused on getting a clearer sound, I think it sounds better than my previous attempt.
https://mega.nz/#!7Q12UKJI!_UQuW057Qspq4886JivrUaX-M4N1GCzNl0AdKrhL4R8