The above posts make great reason to consider the 308. Out of the ones you had "narrowed it down to", the 7mm rem mag is known for long range accuracy and very flat shooting.....as is the 6.5-284.
6.5-284 will have less recoil and alot of guys shoot them without a brake and find it plenty shootable. Downside is not much selection in ammo yet. Probably have to handload for best results..........Which is where the 7mm mag shines, there are tons of factory offerings in that cartridge.
On these forums, you'll probably find more opinions on calibers and scopes than you could ever imagine.