Roger,
I cant give you much advise on that leg of the trip because we always skirted around it because we were coming from/going to Canberra. We usually joined that route at about Orange.
I was thinking the other day that it actually IS colder going inland rather than following the coast although I still wouldn't recommend the coast route because of traffic.
I WOULD stick to the highways though and NOT take too many back roads. Back roads are just going to be too narrow and in poor condition. They will possibly be steeper sections too.
Anthony