Answering my own question (re: grass-fed beef in Aus)

"It's important to know that most big-supermarket beef around the country will be grass-fed meat finished on grain, but if the meat comes from southern Victoria or Tasmania, where grass is more likely to be in abundance, there's a good chance it was reared entirely on grass or silage"

Also there seems to be a taste/health tradeoff for grass vs grain-fed beef. wagyu, after all, is the epitomy of grain-fed beef...