Thanks for the explanation, Zak. So for any caliber, a sort of optimal cartridge design could be devised such that the bullet had a BC of 0.6 or higher, and a muzzle velocity of up to around 3000 fps. There are certainly tradeoffs in doing that, though.
Back to the theme of the thread, it would seem the .308 was selected by the military more as a semi-auto cartridge than anything else. Perhaps the .308 made a better semi-auto round than bolt-action precision sniper round, because it represented a good compromise between heft of gun/action necessary to fire it, and ballistics (both external and terminal).
Re: consistency. As I understand it, there are .308 rifles that achieve 0.25, which is on par with other field use rifles. If you get the windage and distance exactly right (a big if), ballistics shouldn't matter, at least until you reach the transonic boundary. Granted, it's difficult to get them right, but given say a stationary man-sized target at 600 yards, a moderately accurate rifle of say 2 MOA, and some moderately skilled windage and distance estimation, you should hit the target all day long with a .308 if you do your part. At 1000 yards, it's much more difficult, but say 30% better ballistics alone isn't going to make up the difference between a hit or miss for significant errors in distance, wind or an innaccurate rifle. Assuming you can get everything right at 1000 yds, things like remaining energy of the round and weight of rifle to accomplish it are important.
I'm just trying to get a grasp on how much the inferior ballistics of the .308 really matter in practical situations.