Slippery Pete, funny you should say that.
we are on the Optus HFC cable and we get 100mbs reliably. The nbn guys installed the prewiring to our house and said “you will love the nbn! The speeds will be great! You should get up to 50mbs!” I said “oh god I hope not!” “Why he says?” ”I get 100mbs at the moment”..”oh you won’t get close to that” he says.
so while the popular opinion is that the Optus Hfc system is crap and a dud buy, it is delivering, reliably, double what nbn promise, so it can’t be too much of a dud.