Have you determined what speed your TV streaming device pulls movies from your Storage Spaces or DrivePool? For example, when I watch my DrivePool GUI, I can see that my Fire TV Stick is pulling about ~4 MB/s tops for streaming 1080p movies. I don't suffer any stuttering or caching on my system. If I try to stream movies >16GB, then I start to see problems and caching issues. But, at that point, I know I have reached the limits of my Fire TV Stick with limited memory storage and its low power processor. It is not a limit of how fast DrivePool can send data over my wifi.
Well, there is how many bars are available to indicate how strong the connection is, but bars does not equal speed. On my old 56K router, I would also have 4 or 5 bars indicating a strong connection, but I was constantly fighting buffering issues while streaming. I upgraded to a 1 gigabit router, which is much faster, and that took care of my buffering problems.
Well, good questions but beyond my level of tech expertise with that equipment. I get my internet service from a local telephone company, and they have a computer support team on staff to answer questions and help customers with their equipment. If you are leasing your equipment from ATT, then they might have a support team you could contact for assistance.
At least you have something that is currently working for you, so it's not like you are in a panic. After years of running Storage Spaces on my system, and now with DrivePool for just less than 1 year, I don't yet understand why you are experiencing streaming issues with DrivePool. On my system, it made no difference at all in regards to streaming, which I have stated runs at about 4 MB/s tops and usually much less on my system.