I’ve given it a tweak, using the normal speed “once thought as you do” and adding a pause between the two parts. I don’t think I like it as much. While adding a “but” between the two lines would work, I couldn’t find a clean enough clip of Jones saying it as Vader.
Here’s the new one. Again, I’m sure Adywan or another sound editor could make it sound cleaner and better edit the music around eliminating “I must obey my master!”