I have taken elk with .270Win, .300Rum, and some 400gr arrows. All have done the trick. The two rifle loads both went less than 5 yds. The arrows went about 40-50 yds. each.
My daughter also took her elk with my .270Win. DRT, not even a step.
I am building a 7mm for longer range deer/elk hunting as we speak. Thinking about the 7mmRem Mag and the 7mm STW. I have had both in the past, and loved each. Leaning towards the STW just for kicks (but with a muzzle break, that kick will be tamed somewhat). I don't plan on shooting thousands of rounds through it, as it will be a large game long range hunting rifle only, so barrel life is not my main concern, but the STW will eat up a barrel faster than the 7mmRem Mag for sure. Maybe twenty shots/year after break in, load development, and sighting in.
In my opinion, anything accurate in the .260-.308 caliber range is more than sufficient with ethical distances and shot placement for elk. Some say the .257 is up there, but that is a little light for my tastes. .338 is a choice too, but damn, that is a lot of bullet. But, dead is dead, and a correctly placed .338 should certainly do the trick.
Bullet construction and shot placement....that is the key to a dead anything. Of course, even a leg shot with a .50BMG will most likely kill an elk.....it will tear it right off and leave a great blood trail, if there is any tracking to do.