Dirty Girls - S7-E18
Xander: I've been through more battles with Buffy than you all can ever imagine. She's stopped everything that's ever come up against her. She's laid down her life - literally - to protect the people around her. This girl has died *two* times, and she's still standing. You're scared? That's smart. You've got questions? You should. But you doubt her motives, you think Buffy's all about the kill, then you take the little bus to battle. I've seen her heart - and this time not literally - and I'm telling you right now, she cares more about your lives than you will ever know. You gotta trust her. She's earned it.
[Pause.]
Faith: Damn. I never knew you were that cool.
Buffy: Well, you always were a little slow.
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