If the playback device isn't terrible (though smart TVs probably are), 100 Mbps should still be adequate as long as the average bitrate stays below that (which I think is the case for almost all UHD blurays?) and you get close to the nominal speed. For example if it peaks at 120 Mbps, then you're only draining your buffer at 2.5 MB/s, so a 150 MB buffer gets you an entire minute of peak bitrate as long as it was full. A quick search suggests very few movies go above 100 Mbps for longer than a few seconds at a time and averages are usually below 80.