I've only hunted elk with a 7-08, never killed one with it. 150-gn Partition.
I will say this. It made me wonder, while I was doing it, WHY I was doing it!
I mean I never doubted that it'd kill an elk (how could it NOT, if I did my part) but damn those are big "deer", and tenacious sometimes.
Elk camps are rife with stories of elk absorbing lead and making the hunter's life a living hell trying to sort out the rodeo. I've personally talking with a young guy a few miles back in the elk woods, tracking a spike elk that he'd shot with his .308, with a strip of lung in his pocket about 6" long that he'd gotten from a log that the elk jumped over... never did recover that elk, and he had snow to track it in! They can be that tough.
Just for the sake of sleeping well at night I use a bigger rifle for elk. I know, in the hands of a good hunter yadda yadda yadda. Maybe I'm just not a good hunter.