I have debated the same 6.5CM vs. 308W topic myself.
What did Heinlein write? TANSTAAFL or something like that.
The 6.5CM with most loads will shoot flatter, drift less, and recoil less. The average shooter may not be able to see a difference in hit probability…but it is there.
If you want to turn $$$ into noise the 308W has bulk surplus ammo offerings the 6.5CM does not.
The 6.5CM will be harder on barrels but few will ever burn one up. If you don’t practice enough for it to matter, you may want to hedge your external ballistic bets anyway you can and shoot the 6.5CM. If you DO shoot enough to burn up barrels…then you are probably good enough to appreciate the added insurance the 6.5CM’s better ballistics give you.
From a terminal ballistics stand point I think you would have to go over +165gr 308 bullets to see any realworld difference in tissue damage or killing ability.
I have killed plenty of stuff with a 308W and I currently don’t own one. From my experience the heavier +175gr bullets kill markedly better than the lighter 150gr and under.
I have also killed plenty of stuff with a hot 6.5mm. The 6.5’s are much less forgiving of bullet design in my experience. So do your research.
A good shooter can do things with the better ballistics of the 6.5CM that you can’t do with the more anemic 308W.
A less skilled shooter needs to hedge their bets anyway they can to get the bullet into the hydraulics.
All things being equal the vast majority of shooters (expert to novice) will shoot the lighter recoiling 6.5CM better than the heavier recoiling 308W.
A good line in the sand for terminal performance is the distance at which a given load drops below its fragmentation threashold. Usually someplace between 1800-2200fps, depending on bullet design. I would guess the 6.5CM carries that velocity threashold a bit farther than the 308W in most cases.
Others are entitled to their own opinion but I do not consider either the 6.5CM or 308W serious elk cartridges. Will they work most of the time under good to great conditions? Sure. Are they ideal? NO!