The 6.5X55 and 7X57 have been taking elk, bear and moose since the 1890's. They traveled the globe and have taken every animal in Africa including elephant for almost 130 years. At some point hunters fell for the advertising hype and bought into the notion that they needed bigger, more powerful cartridges to take game larger than whitetails. The way I see it the rise in popularity of rounds like the 6.5 CM, 260, and 7-08 is hunters coming back to their senses.
It is my opinion that none of the Creedmoors shoot heavy enough bullets at an adequate velocity providing enough penetration and exits to reliably put down elk in every situation.
The 140 gr 6.5 bullets will match a 180gr 30 caliber bullet in penetration if using bullets of the same construction. That isn't just theory, it's been proven. If a 180 gr 30-06 doesn't give enough penetration what does.
