Would you say it's significantly worse than what you see on high end LCD 4K HDR TVs with the same source material?
In my experience, any higher-end TV will show artefacts on poorly encoded material, as they show so much detail - no TV is clever enough to choose between showing you 'good' detail and 'bad' - it just shows you everything. In my experience, high-end LCDs are more forgiving than OLED when it comes to compression issues.
How do live sports look (and compare to LCD)?
Fantastic. Motion is an absolute joy. As long as you get lucky and get one without banding. If you get a bad one, when the camera pans, any band will show up when the ball travels the field.
You also have to get a decent one with good uniformity, otherwise sports like ice hockey are out, as some parts of the ice will look blue, some redder etc. Not fun.
I was actually thinking of dumping my cable and going with PlayStation Vue. Sounds like this might not be the best course of action if I get an LG OLED because I know the streams are capped at 720p. Thoughts?
This is outside my area of expertise, so I wouldn't have a clue. I would say though, again, that the lower the quality and resolution, bearing in mind the set has to blow up a 720p image to 4k internally, the more likely you are to have problems.
I really don't want to come across as too down on the set - I love my b6, but it is not always sold on the limitations it has, and you have to consider what you will be watching. There isn't a time watching a film or a TV show, where I'm not wowed at least once, and having the TV disappear, during totally black scenes, in a dark room, still blows my mind, but, like all sets, there are positives and negatives to consider.