I can only add the experience of one Elk hunt, but I think it's relevant.
In 2016 I had a one-off opportunity to hunt Asian Elk, in Kazakhstan, and was warned that distances were very long, due to the landscape.
I took my 6.5 Creedmoor and (on the recommendation of a member of this forum) went with 139gr Scenars, loaded to ~2840fps. I had ranging binoculars & a ballistic turret on the scope.
In a week's hunting I had only one chance at a large mature bull, across an open valley, and had about a minute to take the shot as he was about to get up and chase off after a younger Bull. The bullet hit right behind the shoulder at ~590 yards and put him down within 20 yards. To my surprise it also exited.
The other guys in our party had multiple misses with 270 and 7mm rifles, at between 400 & 500 yards (as they had no ranging equipment or ballistic turrets). They eventually got animals at <300 yards.
Rightly or wrongly, my conclusions were:
1. Accuracy/bullet placement is the #1 priority, especially at longer ranges
2. A 6.5mm with ~140gr bullets can penetrate and kill large game animals cleanly
3. I would have struggled to get my Elk if I'd taken a more traditional calibre, like 30-06, 8mm or a 35 Whelan.
