Nathan Foster’s website (Terminal Ballistics Research) is informative - though I’m not sure he’s been updating it much recently, and I don’t think there’s an entry for 6.5 Creedmoor.
He also produced a book that goes into a lot of detail on exactly what you’re asking about - and you used to be able to buy an electronic copy directly from his website.
He’s a slightly divisive figure, with some idiosyncratic views - but he has done a lot of testing and makes his interpretations accessible.
+1 for the Nathan Foster advice, Ron Spomer is also a generaly a quite sensible, fair viewed and experienced source on matters like Terminal ballistics and effect regarding types of projectiles, cartridges, shot placement on different species (in relation to their anatomy) the effect claimed by some of terminal velocity and so on.
For general understanding of how a bullet kills the animal, and how that might change depending on shot placement, or type, size or speed of bullet used, i thinks these pages by NF are as good as any info i have found yet:
Effective Game Killing
As for his opinion on specific cartridges and their TE, i dont know if he has the creed there, but he quite surely has the 308.
He does however have entries for the 6.5x57 and 6.5x55, two cartridges shooting the same caliber bullets as the 6.5 CM , in fastish twist rate barrels (so similar weight projectiles can be used) with quite similar amount of power produced to propel those bullets, so i'd suggest reading his entries for those two, if he hasnt written specifically on the 6.5 cm yet.
Mind you, as i remember his entries for mid sized 6.5s, he's not a huge fan of their killing power at even medium long range, but that is just his opinion, of which he is of course more than entitled. When researching I think you'll find others good sources who think differently, so happy reading (and learning) and of course hunting!

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