Dennis, connect to
http://speedtest.net and check your speed when it is ok and when it is bad, get the figures and complain. If they don't fix it go to the ombudsman and complain. Optus overload their network and shouldn't be allowed to get away with it. I'm on uncapped adsl1, unlimited TPG and I fully expect 1/3 of full speed in the evenings during peak. Optus is often crap during the day which is unreasonable.