I didn't feel that the normal version went well as a fight BGM. The slow version was far more menacing (and sounded vaguely Egyptian, which wasn't helped by the fact that the episode 1 WN looked kind of like a genie's lamp
) and really set the dark mood for the scene. That isn't to say that the normal version isn't dark (it works wonderfully in the ED), but the slower version just fit as a fight BGM there.