On a pig hunting trip where the roos were extremely wary I had a shot at the roos at 600 metres using a 7mm STW ... I mssed of course ...

Roos can be very wary, if hunted a lot. And see or sense you a long way away. Tried bow hunting them once, once they spotted me, they kept me at least at 60 to 90 metres away, if I got closer they hopped away. In close bush of course one could get within range unless spotted.

Most of the 3 to 4 million roos culled each year at shot at night with spotlights.

Where they aren't shot at all, like my own property, they aren't wary at all. Still keep a person 50 metres away or more.

Yes the reds are desert animals and probably would not cope with snows. Eastern mountain greys and mountain euro/wallaroos might do better.