http://testmy.net/download is very accurate. I have seen my connection drop to less than 0.3mbps before and it not pleasant. Even video on the lowest quality settings with youtube or netflix will be constantly buffering.
Hughesnet's speed tests isn't totally defunct, and it often gives correct results, but it can be buggy at times. As imalexdude suggested, and the reps here recommend and request to be used, testmy.net is an accurate speed testing site. To make sure your speed test results are accurate, you should use the 25MB manual test size when you test your download speed and the 4MB manual test size when you test your upload speed. The Auto Test shouldn't be used.
With that said, the Video Data Saver can affect streaming, especially when streaming in HD.