Something I've been thinking about recently. A vampire is stronger when they use their "game face," right? If I remember right, in "Prophecy Girl," Buffy told Angel to use his game face before he fought off the Master's goons, and Angel was able to overpower the Beast and bring him to his knees only after he used it.
I think at one point, Angel said that the vamp face does make him stronger, but also increases his bloodlust. I can't remember what episode, though.