I think the .260 Remington is better. 6.5 bullets fly better. A 6.5 Grendel would be "better" than .308 at distance. So a 6.5mm with a larger case is better yet. But speaking to longer ranges, 600m plus.
For shorter range than I guess the 338 is better for close range just based on bullet weight. However, it all depends on the targets. Just because it has more energy doesn't mean it is the right choice. There is video out there of people using a .50 to hunt and that didn't work out like they thought.
Than you have factor throat erosion.