When doing a speed test, I generally get faster than expected results. I pay for 50/5, and usually test around 55/6. However, during peak times I frequently have issues with Netflix and Youtube videos. These issues don't exist with other websites I've tried, and speed tests still show faster than expected results.
After getting frustrated with poor performance in the evenings, I decided to set up a VPS running an HTTP proxy. When using the proxy, all issues with Netflix and Youtube go away and I get the maximum quality available with no stuttering.
So at least in my experience, Mediacom seems to be engaging in the same shenanigans as other providers. I've noticed that at least in my area, Mediacom seems to be using AT&T as an upstream provider so this could just be AT&T screwing with things. Either way, I'm not happy that I have to go out of my way just to get a usable connection for internet video.