Think in terms of time rather than distance.
Lotta elk just wander away while hunters are fiddling with scope dials.
If you hunt on your feet you'll mostly see elk at more-or-less the same time they see you. I read once the average elk kill distance in Colorado - 93 yards. I believe that statistic to be very accurate.
You might have 3 seconds, maybe 5 seconds. That sounds dramatic but it is actually plenty of time to get into a position and be sure of your shot.
The best elk hunting drill I know is - get your rifle off your shoulder and quickly get into position - standing, sitting, kneeling (prone probably won't be an option because there will be too much deadfall and low groundcover).
You won't have time to scout the nearby terrain for shooting rests - this has to happen wherever you are right then.
Once in position that should still you leave a full second to select the animal that presents the best shot, make sure you have a checkmate shot, and to take careful aim.
Be able to hit a basketball sized target with the 1st shot, cycle a cartridge, and hit again with a quick second shot.
Don't be that guy who is picking up brass instead of seeing which direction the elk went. Whether your shot found it's mark or not you will want that brass left on the ground as a reference.
If you somehow find yourself in a situation where an elk has broken cover at 300 yards in daylight during hunting season expect there to be some reason for it. Is it private land? special early season? an alfalfa field? busted out of cover? Anyway, if you are that lucky then you will probably have plenty of time to set up for that shot.
I hope you are that lucky.
