Factory 6.5 cm shoots bullets almost as heavy as most factory 7/08 loads. Because they are longer, they have a higher BC, which means less drift and drop. Can also have higher velocity.
If you hand load it can become more of a toss up. But, at long range the 6.5 wins at precision for the most part. You can't hand load the high bc 7mm bullets unless you have an 8 or 8.5 twist barrel.
Truth is they are so close as to be indistinguishable inside 500 yards. You won't lose a deer because you chose one over the other.
You get into minor or absurd differences like man-bun factor, store availability of ammo, or barrel life. That's what it really comes down to most of the time in these discussions, personal preference.
If you want to shoot long range, factory 6.5 cm ammo is better, cause of the bullets.