Engage YouTube, Hulu, NetFlix, etc in your tests.
This could also be determined on how these websites set up their servers.. Reddit has a reputation of taking down websites when something is popular on there. These popular videos might be kept on one of their servers the. That one server be bogged down by massive downloads on one specific download. I've only noticed this because sometimes only specific channels are slow to load for me.
Jeremy McEntire commented
Of course, the embedded data would have to be hosted on their domain and be indistinguishable by any traffic shaping algorithm. That is, you can't simply do an include on .01% of page loads to fcc.gov/sneakyTest.js -- that'd initiate a fresh connection to your servers and wouldn't necessarily suffer the same issues that streaming video data from YouTube has. I'd like to see YouTube stream a video to the user and report back the time to complete. Maybe they can replace every 100,000th video with a message from the FCC -- much like you have mandatory emergency network tests on TV.