Originally Posted by Unlicensed Dremel
all you need is a credit card and internet connection to dial up Midway USA(and patience til they're in stock), so I stick by my advice on chambering. Though .308 isn't terrible choice, of course.*
Midway offers 170 choices in .308 ammunition, and only about 34 choices for the 6.5 Creedmoor and .260 Remington combined. 40 of those 170 choices is for target/match ammunition so the .308 still has more choices than the others. I'm not arguing the .260 and 6.5 CM aren't good cartridges, just that the .308 isn't lacking either.
IMO the .308 Win is never a poor choice, and you're more likely to find it outside of the web retailers as well. Shooting instead of waiting on a backorder is always a better choice as well. It's kind of hard to learn the skills necessary to shoot to 800 yards with no ammunition to feed a rifle. It won't always be looking the best or cheapest ammunition, but the OP is more likely to find a larger selection of .308 ammunition locally than either of the cartridges you mentioned.