The problem turns out to be the web page itself.

Some thing is either very wrong with the web page, you need a better browser or something else was running in the background that affected performance. My "slow" AMD FX8320 computer is able to use the Rogers speed test page and the numbers I got are about what I expected to see. One should not need a "fast" computer just to run a speedtest.

The only reason I just thought of is that perhaps your internet speed is exceptionally high and that makes the speed of your Internet connection sensitive to the browser and your computer system.