Ok, I am going to assume range / target use. 300 to 600 yards, both the 6.5cm and the .308 are good choices. I would choose the .308 strictly based on ammo cost and availability. That changes if you reload, with the 6.5cm being a more pleasant round to fire.
I would go with a bolt action. AR's can be accurate, but dollar for dollar, your best chance for a truly accurate rifle is with a bolt. Savage, Remington 700, Tika, Bergara, to mention a few, all make target models that are proven accurate. A Good trigger and an adjustable stock are good options.
For glass, a good 4x16, or 6x24 scope would be a better choice than a 3x9. Leupold, Burris, Vortex all make good glass with lifetime warranty's. A good front rest or bipod, along with rear sandbags are needed as well.
So, what was my answer to your question?
A Bergara chassis rifle in 6.5cm (Under $1000.00), Vortex 4x16 FFP 30mm scope ($325.00), Talley one piece mounts and a Harris bipod. 1 1/4 inch 5 shot groups at 300 meters with cheap S&B factory 140 grain ammo, slightly under 1 inch with my handloads using Serra 140 Matchking's. Lots of bang for the buck.
Larry