I don't live that far north, but most people you know that shoot a lot of them (farmers, rangers, jackeroos etc) use 308 Winchesters and factory 180g ammo.
Personally I'd want at least a 30-06 and a premium 200g bullet. If I was doing a lot of it on foot ( ie up close and personal ) a 375 would be better.
When I sold my 338 Win (a Vanguard) a fellow from the Northern Territory bought it by the way.
