Like everything, depends on your expectations. Elk killed with 6 Creedmoor (or 243) every year but bullet selection and most importantly shot placement is key. I'd personally opt for a 6.5 Creedmoor if elk was in my mind as a possibility. Not much difference in recoil but ability to run 140+ grain bullets like the Berger 140 elite hunter or Hornady 143 eldx or others.
My favorite hunting rifles for small to medium game are my 6 creedmoors with 105gr Berger Hunting VLD's.
But when asked by friends what to build/buy, between the 6 and 6.5 creeds, I always ask, "are you going to hunt elk with the rifle". If answer is "yes" my answer is 6.5 creedmoor. The 140 class bullets with the 6.5 creedmoor simply provide's more energy than a 105 6 creedmoor.
With that said, I'm fully confident in my ability to place a shot perfectly, and the effectiveness of the 105 Berger, to take a shot at a cow elk to 300 yards.
For big mule deer and antelope, a 6CM would be great at moderate ranges to 600+ with the right bullet.
My opinion, a 6CM, or any 6mm/.243 is light for elk. I am sure they will die fine with perfect shot placement at moderate ranges, which we all strive for. But it would suck to see a big bull across a 700 yard canyon and be undergunned for it.
Thank you all for your responses so far. 700 yards is a chip shot for most of the guys on this forum. Heck, I still think 400 is a long shot for this old bowhunter. From the sounds of it, I am needing to rethink this project.
Like has been said, the 6mm Creed is about like a .243 Win with comparable bullets. The 6.5 Creedmoor is about like a .260 Remington. I remember a time when a .260 Remington was considered marginal for elk. I suppose all of that changed with the premium bullets we have today.