I just wanted to add my two cents. I was going to post something just like this. My wife and I have the Ultra plane, 50/50. Last month, using youtube, and a couple of Hulu TV shows, using the internet like crazy. Downloading PS4 updates (900mb-5GB in size), we have still managed to have around 63GB total remaining!
We manage our network well, no data leaks, shut devices off when not in use, and make big downloads after checking our data. I also downloaded the biggest update when our data was about to restart for the next month.
OUR INTERNET IS FAST! shhhhh.. don't tell anyone but we still average over the up to advertised speed of 15Mbps. We get a little slow down during peak time 7-10pm, but the slow down is still faster than the Frontier DSL we used to have at 0.50Mbps.