just stumps, ant hills squirrels and grouse for me. As far as penetration, you'll be better off with with either head, cause neither will give any more then marginal gains over the other, just shoot the one that gives you confidence. If they are the same style of head, don't fret over it. Just make a good solid shot.
though yes, in theory, a narrower head, given all else equal, will penetrate deeper, having less friction. Elk are only a couple feet wide though, so the argument, IMO is largely moot.
enjoy the pursuit!