I think caliber and bullet weight gets debated way to much over the internet. Elk are not hard to kill if you hit them in the vitals. I shot a bull elk this year in colorado at 450 yards and dropped it in its tracks. I shot it with a .270 WSM and a 110 grain Barnes TTSX bullet. Thats the only elk ive ever dropped in its tracks. In 2006 i shot a bull at 80 yards with a 7mm rem mag and a 150 g Swift Scirocco bullet square in the lungs, it spun around and i shot it in the lungs from the other side and i was about to shoot it again when it fell. If you happen to hit an elk or any animal for that matter in a critical area it may drop in its tracks but that doesn't always happen. Bullet placement is way more important that bullet and caliber choice. Choose a gun and caliber that you can shoot good and is reasonable for the game you are hunting, practice shooting it and know your ballistics well and you'll be just fine.