IMHO, Speedtest.net is not an accurate prediction of your bandwidth over time.
For example, I just DL'ed Mac OS 9.2.1 update which is 82MB. It took 76 seconds. This translates to a 1.08MBps or 8.63Mbps rate.
My ADSL line is rated at about 45Mbps. As usual with ADSL, the actual speed is much less than advertised.
In this case, Speedtest.net indicates a 5,499kbps which is not near the 8,631kbps rate that I am actually getting.
YMMV.
That is why I recommend DL'ing the Mac OS 9.2.1 update or some other large file (at least 60MB in size) and time it. That will give you a more accurate reading of your actual speed at that time.