Tenebrous vs. Exar Kun

Exactly. Vader probably can't run nearly as fast as say, Qui-Gon and Obi-Wan did in TPM but he's still faster than them in terms of combat speed and a better duelist overall.

Plagueis turned Venamis duel into training exercise when he wanted to. Then Venamis accepted Plagueis superiority and called him ''master'' , Plagueis probably is not fast as peak Sidious, but he has other tools to compansate.