Everything you have has enough punch to kill an elk. Shot placement is key, though. Elk are extremely tough. Last Fall I have seen a cow elk get hit broadside at 300 yds. by a 30-06 and walk away. Searched for hours in the dark. Minute blood trail, everyone thought it was a miss/minor injury shot. In the end it wasn't that. Found the animal next day. Perfect kill shot shredding the lungs, the bullet just hadn't exited out the other side, that's why not much blood.
My point is to pick the rifle/caliber combination you are most comfortable with to hit the target at a range of distances, 200, 300, 400 yards to minimize the second-guessing. Having experienced a few elk hunts myself now I wouldn't expect to come within 100 yards of one.
And as an obvious side note, a big Magnum round is more likely to pass through, and even if the animal walks, it will be easier to track.