I don’t know, I was just watching Empire Strikes Back the other day, and actually it’s pretty surprising how calm and reserved Vader is most of the time. In A New Hope Vader loses his temper once, in the very first scene, when he’s like “Tear the ship apart and bring me the plans!” or whatever. But in Empire he’s very subdued. He never loses his temper - he just calmly kills you when he feels you’re under-performing. The closest he comes to sounding angry is when he says to Ozzel “You have failed me for the last time, Admiral”, but in fact he barely even raises his voice when saying this. He just wants Ozzel to shut up so he can tell Piett the plan going forward. He comes off as ruthlessly efficient, which goes along with his “half-machine” persona.

Sometimes Vader sounds a bit impatient - it’s kind of funny when some Officer has to bother him when he’s inside that meditation chamber, and Vader is like “What is it, General?” You can hear slight impatience in his voice. But he never rages or loses his temper. He’s the complete opposite of Kylo Ren. And definitely way more subdued than Anakin, who was constantly flipping out in both Episode 2 and 3. We can make excuses for this personality difference by saying that over the years Vader became more mature as a Sith and learned to channel his anger in more constructive ways or whatever, but honestly the reality is that Anakin’s portrayal just kind of sucks.

Also of interest to continuity is that Vader is slightly different in A New Hope because he essentially was a different character at that time. He was written as more of a generic villain who killed Luke’s dad. It was only with Empire that Vader became a more complex character, and his personality changed slightly to reflect that. But the difference between Episode 4 Vader and Episode 5 Vader is barely even noticeable compared to Prequel Anakin versus OT Vader.