The best spell for killing an enemy is Cold Snap as you can play it as long as you got ice man. My killchain at the moment is Sneak Attack, Magic arrows, 4x Cold Snap, 2 attacks (sometimes the second isnt working). So 7 kills for every enemy =)
Realized it too late, but the trick with the elevators is to make them a maximum of about 6 floors or something and then begin a new shaft, so they have to change the elevator... Then they will wait more effectivly, but in many small phases so they dont feel disturbed by it...