There's a lot of good reasons to choose a 6.5 over .308 as the ballistics are simply better beyond 600 yds. And I feel 6.5's are much easier to reload cartridges that produce lower ES's and SD's too.
I chose to go with .308 and I'm glad I did these days given how hard it is to find supplies for 6.5's as opposed to .308's.
And, my .308 with a Krieger barrel (my second barrel) currently has over 5,300 rounds though it and I'm still getting bugholes and I have fun shooting out to 1000 yds when I can. Had I gone with a 6.5, I'd probably be getting ready to put a 5th barrel on.
A buddy of my that I shoot with has a 6.5 and as much as he loves shooting that gun, he limits the amount of shooting he does with using mild to moderate load to save barrel life.
So, which to choose really depends on what's important to you and just what kind of shooting one is doing and don't mind changing out barrels more often if one is doing a lot of shooting.