The 5.56 only does well because the standard comparison test is normally ballistic gelatin blocks. This in my mind is not representative of human torso's. Its too soft and as the 5.56 tumbles easily it always results in larger wound channels, but this doesn't equate to better stopping power in the real world. Better tests would be against animals, but this is not pollitically correct, is messy and hard to control scientifically, so the gelatin block keeps getting used.

The 5.56 only has half the energy of the 7.62x39 at around 500m and thats for the longer barelled versions that no one uses anymore. Some M4 barrels are down around the 12-14" mark these days.

I would feel undergunned using 5.56/.223 on goats and I'm not alone. The SSAA Hunting and Coservation club sets the minimum for goat culls as .22/250.

If I had to put my life on the line, I'd want the stopping power and range of a 7.62x51 for most applications apart from close quater battle.
George