When To Choose A .308 Over 5.56?

[TehLlama]

How effective is the 223 M855A1 on a no body armor target at 600 meters vs the 7.62 x 51 M118LR?

At that particular range and those particular loads, that's an apples to watermelons comparison - smaller caliber semi-penetrating projectile against a 30 caliber reverse drawn open tip match projectile that deforms across an impressive range of velocities? In the cartridges in question one is already down to the sub- 1.5 Mach region where some bullets don't seem to want to deform or yaw, while the larger projectile is already traveling at a higher speed [almost exactly Mach1.5 @sea level ~625yd] and in a design that is more likely to either deform or yaw after encountering soft tissue.

Comparing more similar setups (Mk318 62gr 5.56x45 to Mk319 130gr 7.62x51) [Mk262Mod1 77gr to M118LR 175gr] would yield less divergent results.

At the rate this discussion is going, I'm really going to want to figure out what realistic soft target testing has been done with these projectiles in velocity equivalent analogs to longer range terminal effect - this information alone may sway me towards wanting to run a battle rifle (read 16" 7.62 gas gun) for basically everything between 400-800 meters unless I'm hunting exclusively paper and other inert targets).