The best use for a DC10/747 would be in creating fire breaks. Otherwise, we'd need the fire to burn in a straight line for them to be most effective.
I agree with earlier posts regarding amphibious aircraft, there's just not enough lakes & rivers they can use. As for Port Philip Bay, well, who wants to tell a Farmer that they just dropped 20,000lts of sea water on their land?
Personally, I think our chopper pilots do a sterling job, all things considered and you cannot underestimate their accuracy when compared to fixed wing solutions.
Just my 2 cents worth.