I didn't get a response to my original post, but I thought I'd provide an update...
Having experienced nearly three weeks of having dropped from a stable 40Mpbs connection down to a consistent 1 to 2 Mbps, and my ISP telling me that there was nothing wrong with the connection that they were providing, my modem dropped the connection this morning... then came back up at 40Mbps. It's only been back up to that speed for a few hours, but it's looking promising!
When the connection dropped, I used my mobile phone to check my ISP's status page and, lo and behold, the carrier was carrying out maintenance on my exchange all day yesterday. I then looked back to when my connection problems started nearly three weeks ago, and noticed that 'maintenance' had also been carried out the day before I started having problems. What an amazing coincidence!
As it happens, a couple of hours before my connection went back to normal this morning, I had already decided to change ISPs (after 7 years) and had signed-up with another provider. I understand that changing ISPs was no guarantee of an improvement in connection, but I did not appreciate the service and information provided to me by my current ISP. Did it really not occur to mention to me, on the first day I contacted them, that my exchange had maintenance on the previous day? Was it really a coincidence that my problems started the day after my exchange had maintenance, and then stopped the day after further maintenance was carried out?
My new provider (to which I should be connected next week) has good customer services reviews, and is AU$10/month cheaper than my current provider, so hopefully, I'll be getting the speeds I am paying for with good customer service, and a sizeable annual saving!
Thank you to testmy.net for a great service. It's much appreciated.
Your account has a memory of your last server selection, when you're logged out TMN also has memory of your last setting... stored differently.
See in your results, when you're logged in you can see your username in the result. On those results you also see a star standing for the Dallas TX locale. The others are testing against servers in Australia. While logged in visit the test mirrors and select au.testmy.net.
The next version of TestMy.net has mechanisms built in to remember your settings regardless of whether you're logged in or even signed up. It will also track your IP address changes regardless of being signed up or not. Actually, it's already doing this it's just not enabled yet so when it's enabled it will be possible to track your old IP addresses over the past few years.