As far as distance, that would depend upon the shooter and the rifle. On whitetails, I feel as comfortable at long distance with my .308 as I do one of my 7mm or 300 mags. As far as real world effectivness, you could throw the .308, 30-06, .270, etc. all in the same group. The .308 is an exceptionally accurate cartridge plus you have the advantage of very cheap surplus practice ammo.