I'm sorry, I don't really get what the problem is here.
I don't know many controllers who are not mindful of speeds when clearing two to the same level. Too many types and too many operators.
If the V bean counters are stupid enough to fly as slow as they can up and down the coast, let them go. They will screw the slot time up for themselves and waste even more time holding somewhere over NSW burning the shareholders gas.
I realize now how good the airlines have it is australia. Some places around the place you can start you decent 380miles from destination. ATC couldn't give a crap if you decide to fly slow, they will just move you out the way of the big one behind you. And you would have been no. 4 in the sequence but now will be 20, expect holding. Not enough gas, too bad, what is your alternate?