T-mobile actually takes all video streams and reduced their bandwidth. When binge on is active, even YouTube Is "optimized". It's the main reason I don't understand why a provider has to "opt in". Binge on literally "optimizes" all video streams but the opting in is begat allows the end user to have none of that count towards their data pool.
As far as the original question, I've found that you use roughly 200 megabytes per hour streaming YouTube with binge on active.