[Sephiroth]

There are two reasons for speedtest.net being less than useful.

The first is that the results at any time will usually differ as between servers that you choose. Some servers are notorious.

The second is that internet behaviour changes from second to second. The speedtest.net snapshot period is too short to overcome these effects - never mind contention on the server you've chosen.

Downloading a very large file from a location known to have high bandwidth takes minutes and that makes for nice averaging over the period of concern to you.

You can do 10 speedtest.nets on the trot to your favourite server and you will have large variances (usually). That tells you only that the internet is a variably busy place.

So if you point people there as first port of call, they'll be straight onto this forum complaining about problems many of them don't have!