You have gotten some good advice here follow it, make sure your capable of making the shot, make it well placed, don't try and reach to far and you will be fine.
If you wanted a big caliber tropper has it with the 338. I use a 30-06 and so far it has worked just fine on several elk. I don't take shots that I feel are to far or that I am not sure of good placement.
338 Winchester mag. with a 200 grain bullet has about the same trajectory as a 30-06 with 150 which is what I use. A well placed bullet will work better than a huge one not shot well everyday.
I didn't shoot at the largest elk I have ever seen in the wild because he was too far to make a good shot. I might have been able to hit him maybe not. Besides being in a hole I didn't want to try and get him out of there was a good chance I would wound him and never retrieve him. Any good hunter won't take a shot such as that. He was perhaps a animal of a lifetime but still sometimes you need to say "nope not today" and enjoy the fact that you even saw him.
Largest elk I have helped pack was killed with one correct hit with a 7MM-08 using a 140 grain bullet. I am not advising a 7mm-08 on elk but if hit thru the heart and lungs from a good side shot it works fine. That animal didn't go 50 feet from where he was shot.