If you already have a .308, and want to re-use your brass for a different caliber, it would be alot easier to just rebarrel it to .260 Rem or .260 Rem AI and you can neck-down your .308 brass to make .260 brass without any major issues. Or, if you prefer, Lapua makes .260 Rem brass you can buy new.
I personally would choose the .260 AI over the 6.5 Creedmoor...Just my personal preference, even though I don't own any 6.5 calibers at the moment, so my opinion is not based on bias, just my personal opinion as to which one I like better. I hope to build a .260 AI someday soon.
I love my .308....And if you can shoot the barrel out of it, you're doing some serious work. It can take upwards of 10,000 rounds to wear out a .308 Win barrel...Sometimes more. I believe the AMU changed their M14 barrels somewhere around 14,000 rounds, if I remember correctly. That's ALOT of shooting.
I think everyone should own a .308. And I am also an advocate of collecting guns, and NOT selling them. I will never sell any guns, because you can ALWAYS fix them up and make them better, unless it gets runover by a D9 dozer of something. Then it'd be comeplete scrap metal. LOL
I say keep the .308 and learn to shoot to 1000 with it, and it will make you a much better shot in the long run, when you do decide to get one of the faster 6.5's, that will make shooting into the wind a breeze (pun intended