1. Your accuracy at far distance. If you are really good shooter then....
2. Bullet performance, elevation.
3. Where you shoot elk/moose at (lungs, shoulder etc)
Colorado parks and wildlife requires 1000lbs energy left for double lung kill. Recommends 1200+. At 8000 ft elevation, 40f, 180eldm 3000fps from barrel, at 1500 yards still has ~1230 energy remaining. Theoretically, if you shoot good moa at that range, you can shoot elk in lungs. 180eldm at that range still has ~1755 fps left, which is still good for expansion, as eldm expands down to 1500-1600fps.
1500 energy remaining is old school number, and dont really need that much. I seen elk taken with 147 eldm 6.5 CM from 1250 yards, bullet only had ~850 energy left, hit elk in the spine and it dropped right there on the spot.
So yeah, stop listening to those who say you need 1500 energy, and 50 bmg for elk and 300 grain bullet or so. A lot of elk taken with ~140-150 grains, 7mm08. For those who hunt at elevation, even 7mm rem mag is overkill. 7mm08 shooting 162eldm with muzzle velocity of ~2720 at higher elevation is 800 yard elk rifle EASILY. 1940 fps and 1353 energy left. Put it right behind the crease, right there in lungs, and elk is on the table... BUT, you have to be a good shot (for a reason there is a saying that accuracy/shot placement is a key). There been plenty of elk taken even with 243 caliber, which is matter of fact the minimum requirement for elk in Colorado.
However, even if i was world class shooter, i would stick to 600-700 yards.... max 800-850 on very, very rare occasion.