Re: How are the ballistics on a 260 remington.
As evidenced above, the .308 case capacity delivers better LR ballistics with a narrower bore diameter. As also evidenced, there would appear the be a tossup between .260 and 7-08, and I call the toss with the .260 because I personally prefer the available bullet selection.
At LR, I see the .260 delivering less drop, less drift, and more terminal energy than the .308. In comparison it's trajectory and energy delvery are more like those of the .30-'06. But is does it with less mayhem and recoil (a plus), and does it in a shorter action, (maybe also a plus).
My calibers of choice are the .222, .223, .260, and .30-'06, with a recent intriguing interest in the .280 (essentially a 7mm-'06).
While the .30-'06 has a 6.5mm variant I like the 280 because I think it's less inappropriately overbore than the 6.5-'06. In this case, the smaller buller 7mm selection still provides appropriate choices; and my less than average ability to tolerate recoil prompts me to use a lighter bullet to achieve the same result than I would need to use in the .30-'06.
Theories and truths can be misleading, and I still have much to learn about this chambering. But results thus far are positive.
Greg