Revealing mistake: Throughout almost the entire sword fight between Buffy and Angel, from the far away shots, its clear that the actors are stunt doubles. It's very visible when there is a shot from the top. (00:34:05)
Revealing mistake: When Buffy and Angel are sword-fighting, the camera pans up and to the side, you can see David Boreanaz's stunt double. His hair line is farther back then David Boreanaz's.
Answer: She has superpowers, ergo fast movement. The reason she outruns him so easily in "Touched" is that she stops trying to actually fight him and just dodges instead.
Shay