One other advantage of the 223 is speed. 300 to 500 FPS faster than the 308. Can make a small difference.All in all i would go with the 308.
I have shot both at 600 yards and hands down the 308 win's almost always.
If you find that day with no wind
,Then i would give the 223 a good Shot as IMHO it is a more accurate round than the 308.