The Duel of Mustafar

In Star Wars: Episode III, Ewan McGregorand Hayden Christensen (Obi-Wan & Anakin) practiced their duel so much and so long that as a result, the speed that Obi-Wan & Anakin duel (in the completed film) is at the actual speed it was filmed. The scene is better known as "The Duel on Mustafar"