Ok...this is my business per se', but I don't typically get involved due to my typing ability (stroke) but here goes: I work for a company as a broadcast engineer that sells 4K cameras and monitors. (we make the pylon cam)
Please don't take my rantings as a personal slight. 4K is bullshit. No one on this forum has a real 4K TV. I've had this discussion with people bigger, meaner and drunker than me at the local watering hole. I'll get to your question in a second. Television technology has grown leaps and bounds in the last 10 years. They look marvelous. If your eyes haven't already rolled back and said "this guy's an idiot:"
If you are watching cable, satellite or OTA (antenna) you are watching either 1080 or 720P.
Your TV or cable box or computer does the upscaling.(most do it well)
Regarding Pi's question. You should be able to stream and view "4K" (UHD) with 15Mbps download speed. ( do an internet speed test check with ookla or similar. Your results with You tube 4K will probably look better with the the charge for the "4K package, if you have the internet download speed.. I don't mean to be disparaging but I spend a lot of time in TV stations, sports arenas, high end churches and places like that. I still have to sort this out with some broadcast engineers. Without knowing your video stream workflow I Can't be sure of this. I have direct TV and AT&T internet. today I am running 650 Mbps download speed. I have Direct TV and am soon switching to Dish. When we watch Prime I cast it from my ipad with virtually the same quality. Sorry for all the jibberish.
pic for attention....John
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