Consider where and how you're hunting. If you're hunting from horse-back and will only carry the rifle for short periods of time while stalking, and then making long shots, get the magnum, and I recommend the .338mag. The recoil difference isn't that great. The "flinch" on impact is greater with the larger bore. Otherwise, the elk either run off with a bad hit, or drop with a good hit.
If you're walking long distances in the tall mountains, I recommend you just stick with the .270. After all, elk aren't bullet proof. You just need to stick a 150gr Nosler Partition where it matters.
I've got a .300RUM, but when it comes time to hike 5-7mi from camp to glass for elk, and then stalk 3-5mi, and then hike 5-7mi back to camp, it's my 7lb 7mm08 or .30/06 thats gone for a walk. (If it's thick, the short 7mm08, if open, the long barreled '06). The 10lb .300RUM or .338/06 stay at home. This coming fall, the .338MarlinExp. at 8lbs will make the trek. It balances in the hand better than any of the bolt-actions.....