To get an accurate idea of your download speeds you need to do multiple file downloads from several websites at the same time.
For instance:
Start 2 simultaneous downloads from the VM demo games server plus 2 simultaneous downloads of Zen test files.
That's four file downloads happening at once!
Now add up each of the four download speeds to get your accurate download rate.
If you believe that your connection has been Traffic Managed (also called STM, traffic throttling or shaping), check your *upload* speed -- if you're able to upload faster than 128kbps (or 16kB/s) for M (2Mb) and L (4Mb) connections or 192kbps (or 24kB/s) for XL (20Mb) then the slow-down you are experiencing is almost certainly not due to being STM'd.