so what i have learnt i needed a 5mbps line to do a 1080p 5.1. so theoretically you would need a stable 20mbps line however. as soon as anything else happens on the line the quality would go down so a 25mbps line would be required to allow the buffer to run a bit faster.
I have a 20mbps VDSL line (Axxess) and rarely have a problem with Netflix UHD. This is on a Samsung SmartTV. Actual speed using the Netflix speedtest utility (fast.com) is usually 18mbps. Amazon UHD is okay but not anywhere as good as Netflix.
Just an FYI - if you are streaming to a PC, then the only browser that actually outputs in true 4k is Microsoft Edge (windows 10 only).
The apps that run directly on a smart TV are fine, but in windows there's a hardware issue that restricts the video decoding that the GPUs can do.