My cable speeds have been horrible since i moved house (was perfect at my old house), an issue which i never really got investigated as i was told via online chat i would have to call the support line, and never got around to calling.
I am hearing the existing Netgear CG3000 modem has been replaced by Netgear CM500V - is this an upgrade that is being applied to all customers? This upgrade would potentially resolve some issues providing the cause of the problem is not an overloaded node.
I suggest you contact optus technical support to see if it is congestion in your area, another way to tell is that connection speed is good at off peak and crap during peak hours. Any how, contact Optus support via Live Chat and start troubleshoot. There are many areas that could cause the speed issue.
1. Bad modem.
2. Wifi congestion in your new home.
3. Bad wiring
4. Bad computer/devices.