Went Roku years ago and never looked back. We had DSL at our old house, I think 5Mb/s, but had no problems. No 4k TV, no 55" screen though. Only one device running Roku although we never had a problem watching a movie and casual websurfing at the same time.
One nice perk of cutting the cord was that after about a year we had no idea what was hitting the movie theaters--nor what the latest and greatest TV show was. Cutting the cord cut the commercials too. On average I watch maybe an hour of TV per week. My wife watches a bit more but she has several series on DVD (remember those?) that she has had for years and that she can put on while doing cooking, sewing, whatever.