I have now had my V6 for almost a week and thought I'd see what its actual internet bandwidth is.
I have a 100M cable package
1stly Most On demand content such as Sky movies, does not use your internet connection.
As far as I can tell its only the apps such as iPlayer that do.
Watching iPlayer HD (well best quality which I assume is HD) peaks at 26679Kbps with an average of around 10000Kbps
Watching the iPlayer Ultra HD test peaked at 69662Kbps with an average of around 20000Kbps.
so HD could probably get by with 15Meg and Ultra HD 30Meg. Not sure about 4k it has roughly 4x the pixels of HD, but then also depends on compression etc.
Unless something has changed recently iplayer (I gave up on it and tv in general) is still only 720p anyhow.