Any of those calibres are ample for almost any game in Aus. As others have pointed out the .308 is a proven good all-rounder. Pre Port Arthur, I had a H &K 940 30-06 auto. It was an absolute "beast" of a firearm. Interestingly, I used to buy "practice" ammo at the local Aussie disposals store. Machine gun belt 30-06 ball. From memory, it was about $80 for about 200 rounds. It was generally date stamped 1942 to 1944. How times have changed.