Been streaming 4K (UHD) contents from US Netflix for a few months now. Currently 25mbps (on average) is sufficient for UHD. However, even with 25mbps, it takes a bit of time to buffer, e.g. watching UHD shows, you will notice quality when show starts is like SD, a minute later like HD, 2-3 minutes later only UHD... after that its UHD quality all the way until you switch shows (provided you own a UHD TV)