For Peter G:
I may have been unclear about wifi congestion. What I meant is that 'congestion' arises in locations where there are (too) many wifi devices, particularly if they are using the same wifi channel.
Where I now live, there appear to be few wifi users and even fewer 5 GHz users; I use NetStumbler to survey my environment. Before moving here (before NBN), I lived in Sydney in a large block of townhouses where it seemed that everyone was using wireless G (2.4 GHz). The result was that there was wireless congestion at the times of day when everyone was home (night, school holidays); at other times of the day, there was far less congestion. At times of congestion, manually selecting a 'quiet' channel did help.
One rather curious observation here is that most Telstra signals (they are obvious as they haven't changed their default SSID + Telstra Air + FonWiFi) use the same 2.4 GHz channel at any one time, and they are all using 5 GHz channel 36. My Sagemcom always defaults to a different 2.4 GHz channel (from almost every other local user) and always uses 5 GHz channel 149. My settings are both auto. So, auto 2.4 on the Sagem appears to work as expected, and channel 149 is preferable because it has a much higher power output than 36 (and has 80 MHz channel width). Channel 36 would be preferable in a noisy wifi environment - Telstra appears to default to it for the obvious reason in a large city.
 PS: Forgot to mention that my son, who lives in an inner Sydney suburb and has the Sagemcom AC plus Fetch Mighty, has 'congestion', pixellation, and buffering. He is on ADSL, which may be the culprit. However, he says the there is significant wifi congestion around him as he uses devices that aren't dependent on ADSL - in his words 'everyone is using wireless AC'.
@newline (PS hit the @ symbol and select a name and that person will get a specific note you've replied - its quite nifty)
Understand now, wifi congestion. And yes, that could definitely be an issue in any built up area.
My first suggestion for diagnosing is almost invariably to turn of the wifi and confirm the issue over a cable. If the issue goes away then you can saftely move on to locating the problem locally.
Thanks for the hint - I like to learn something new every day and now have done so, today.
There are an awful lot of posts here and at whingepool about NBN 'congestion'; complains are not limited to Optus. The important things missing from many of them are method of connection (wireless/wired), modem-router model and, modem stats (attainable rates, actual rates); many of the available modem routers are sub-optimal - I believe that the Sagemcom is reasonably good. As a consequence, interpreting the complains is difficult. That is why I suspect that many issues are the result of the complainants' wireless environment.
For completeness, my rates are presently 143/48 attainable, 107/44 actual, and they are consistently about those values. However my speedtest results are variable, but never horrible. I have everything - including Fetch - connected by wireless, so my speedtest results are pretty good considering that wireless is half-duplex (unidirectional); presently my Optus speedtest is 95/38 with 15 ms latency. So, my results indicate that the NBN segment of my connection is good and my path to Optus' servers is also good. Thereafter, I am in the lap of the gods and my statistics are irrelevant. That tends me to believe that the second reason for complains is the consequence of the path beyond the RSP's server.
BTW, the only reason I use the Sagemcom is that I retained my landline because of the package I obtained. If I cancelled my landline, I would probably use a better modem-router - one that was cost-effective.
Orange NSW 2800 - Telstra territory. Optus internet here is excellent - the only negative is distance to node (exchange for ADSL) - I'm 195m Cu distance to my node. Optus mobile coverage out here is also superior, but most are happy T$ customers.
 My POI is Dubbo. Optus appear to have sufficient CVC there, now. I'm unsure how many out here have changed over: if it's few, things could could go downhill around next April. The Orange thread at whingepool has been quiet, so seems like local whingepoolians have no complains.
Pixelation of FTA channels when antenna is connected to Fetch (Mighty) STB may be the result of the STB's requiring a stronger signal (input) than the TV, for purposes of recording. If all is OK when TV is connected to antenna, then pixelation when antenna is connected to Fetch STB is likely to be the result of low signal strength; signal-to-noise ratio on the antenna output is another possibility.
My theory would be you're in a nice semi outer population area. Possibly not many heavy downloaders (yet). Also if the historic bent was using Telstra then the end result might you're not competing with too many people (yet) for CVC.
Here's hoping it keeps on keeping on - always refreshing to hear a positive NBN outcome.