penetration, penetration, penetration......ya can't get too much penetration. A good fixed will out penetrate a mech., all other things equal, any day of the week, and on a big elk, I'll take all the penetration I can get.
Some guys use mechs. with success, BUT some guys are pulling high poundage bows too with a lot of energy so they can get away with doing so. I'll take a pass through with a good fixed blade every chance I can get it.
An elk is NOT a whitetail.