I would suggest getting the idea of just dropping elk out of your mind until you get some under your belt, I see more wounded elk because guys are trying to just drop them but don't know the anatomy or shot placement for it. Elk are not hard to kill but they are a heavy animal that can decide to live longer than you want, a 7 mag with a 140 gr class bullet would not be on my list regardless of bullet type, even 168's I would be careful with, your weight to frontal area is too great from a light 7mm bullet. The 6.5 140 Berger is a good penetrating bullet that opens well enough to do some serious damage when placed behind the shoulder which is what you need for elk, don't try to pull of a video production shot cause they fail more times than many will admit on elk, deer you'll straight up pole axe them and elk will drop then in a few minutes their back up and then they can get hard to kill.
Shot placement trumps everything on elk, to just straight up power down an elk takes some major fire power or precise placement severing the spine.