I am disappoint
This was a prime opportunity to fire up the Reg's Online Standards convertor, so that we could definitely quantify the distance between Sydney and Perth.
I'm happy to say that I've now gone and done the appropriate >clickety<, and can confirm that you can actually fit 355786.9617 double-deckers between Sydney and Perth.
Bit of a shame about that last 0.0383 of a bus, but a quick bit of angle grinding'll soon sort that out...