Accurate barrel life for the 6.5 Creedmoor is roughly between 2,500 to 4,500 rounds depending on how hot the barrel gets and what kind of powder is being burned in it.

308 Win. barrel life is anywhere from 4,000 to 7,500 rounds. Again all depending.

Factory ammo for both is very good especially Match ammo. On average the top tier Match ammo for both will be similar in price, tho the 6.5 CM is usually a few bucks cheaper per box.

308 Win kicks more than the 6.5 CM and recoil always handicaps pure accuracy. Not to mention shooter fatigue.

If you don't mind the recoil of the 308win then that's what I always recommend because barrel life is very important for me. I shoot 3,000 to 4,000 centerfire round every year so I rotate several different rifles to make them last.