While many find the .223 to be a mild cartridge - lacking the necessary knock-down you would hope from a miliary round, .308 seem a bit much for a high rate of fire. I like it in my tricked out M-14 for single long distance shots, but it seems like it would be tough to handle on full auto. Although that particular cartridge was suposed to replace the 30-06 which was completely unmanageable on full auto.
I bet a .308 out of a 16 inch barrel is not all that hot.
I think most of us would agree that we'd like something between the .223 and .308 for a service rifle. I know I would. Our Special Forces folks have been working on a 6.8 mm round, I believe, and it sounds like a good idea.
Full auto .308 in a hand held rifle is a bit much for most. I heard stories about full auto fire in the FN FAL. Unless trapped by an enemy squad in tight formation in close quarters, I prefer semi auto .308.