Looks like I might be late to the party... but I also built a speed test that uses Akamai to see how long it takes to download the 10Mb file.
WALDXL - Download Speed
This datasource will run a PowerShell script that downloads a 10MB file and then figures out the speed in Mbps that it was downloaded.
CAUTION: This datasource will download a 10Mb file for every Windows machine specified in the applies to field(default is not applied),every poll(deafult is 20 minutes), depending on your environment this could raise the price for your monthly ISP bill. Specifically, if your ISP speeds ramp up when needed.
I would recommend applying this to: hasCategory("speed") and isWindows()
Then, of course, you just need to add the system.property of speed to any Windows machine you want to monitor Download Speed on.