Funny you mention that. I was in the 6.5/7 prc research camp as well, as recently as last month.
the majority of arguments I saw to pass on 308 or 6.5 creedmoor and go to 6.5 or 7 prc were "not enough gun past 500 yards" for elk hunting.
Then I did some more research. Every bit of data I found showed that the average elk hunt distance was WELL below 500 yards to begin with. 325 yards was around the max distance I got out of every response I summed up and averaged in every hunting forum I could find..and the amount of responses that was at or above 500 yards was laughably low.
This "not enough gun" bullshit is just what some portion of the hunting consumer will always use to excuse poor shot placement.
Adam at Who Tee Who does well with spread sheets and drop graphs. All calibers are within an inch or so of each other to about 500 yards. Past 500 yards, 7 PRC pulls away in performance as far as having less drop and, of course, that lovely BC.
So, really, that means you could do long range targets with it. However, it is a magnum round and has a bit of muzzle flip. I know when I shoot, I keep my eye in the scope but it may take a second and scooting the rifle an inch to get back in view.
And so, I think plenty of guys are going with 6.5 CM because it has less recoil and muzzle flip if just shooting long distance, though I know some are hunting with it. In target shooting, one is just punching paper or clanging steel, no animals are wounded in that process.
And I have seen a guy take down a moose with a 6.5 CM. I would not. I would bring my 7 PRC or one of my .308s.
As you have seen, even with elk hunting, most people are not even getting past 400 yards. So, that depends on the metric one choose for impact. Is it energy or velocity? Velocity is important for expansion of the bullet. Too slow and it may not open enough. Here is the thing I have learned. Different bullets, regardless of caliber, do different things at different distances because of the impact velocities at those distances. For example, a bullet that works right at 300 yards may not do what is needed at 600 yards because of the velocity.
People tend to think in energy, sometimes. For example, Google will show that the wildlife department in Colorado recommends at least 1500 ft-lbs of energy on elk. But you could have a high energy bullet pencil through if the bullet does not open up and do some damage. OTOH, there are some who swear upon using monolithic copper because there is not a jacket separate and shatter, it is more likely to stay somewhat intact and create an exit wound.
So, the reasoning for some about using at least a 7 or even a .30 cal is to have wider diameter projectiles impacting, though not that much wider.
I have not been western hunting. But there are mule deer in my state and the state has a drawing to win a mule deer permit. And they advise being competent to at least 200 yards. the hunt is in a canyon that no trees, just rocks and scrub brush. You get assigne a compartment and safe direction of fire.
I have seen some long range hunters hitting the mark.
I also have heard about people wounding animals and I have not seen documentation of that, just anecdotal.
But I also have read the statement that a sharpshooter can shoot a 1 MOA target at 1k yards but a hunter harvests game at less than 300 yards.
I had a long discussion with someone about the ethical distance. After much teeth-pulling, I got him to stand solid on 400 yards.
My comfort zone is 300 yards and where I hunt has distances averaging 50 - 70 yards through a lot of trees.