Okay well first night of torture test is done and this set is definitely a keeper for me so long as it doesn't crap out in some way
Straight away I'll say that the flashlightng is much more noticeable in a dark room. On my set it's worse down the left side than the right (the right has almost none), but not that bad that I would exchange the set. I checked a fair bit of 16x9 content including some pretty dark stuff, and only on the very very darkest moments could I really notice it on the left side. On 21:9 stuff it was a little more of an issue as the black bars obviously give the bleed a "clean palate" to muck up. Still, it wasn't bad enough that I would exchange the set. Btw the black bars during 21:9 were not otherwise pitch dark. I could see them in the room though they were not objectionable and were definitely darker than the ones on my prior 70" Vizio.
On PS3 screens (eg black but for a white Play icon or the like) it was easily noticed as well of course, and on credit rolls. But with actual content there was nothing that I would object to. I would try to capture the degree of it on camera but I'm positive I don't own a camera accurate enough to get it right. Though there is flashlightng I don't otherwise have any clouding problems that I could really see.
One slightly annoying this about the PS3 is that in between all the BR splash screens (eg fbi, interpol, loading, etc) it sends no video signal. Though the hdmi handshake stays firm, the set does turn off its backlight for a beat. And of course when it does so it gets completely pitch black. Then the ps3 sends a signal and it lights up again. Kind of annoying but I did not notice this (ie backlight shutting completely) during any viewing, regardless of what we or wasn't on screen.
I ran through some scenes in Avatar and they were absolutely breathtaking. Band of Brothers looked incredible as well, as did the opening sequences of the lotr films (even with the flashlightng in the black bars). Fringe on BR was outstanding as well. I also went through a bunch of different cable channels and can say pretty conclusively that this set is very dependent upon source quality. Some looked amazing. For example YES during the Yankees game...wow. The close ups especially of the batter were incredibly sharp and detailed. ESPN in studio looked similarly amazing, though the clips they played varied greatly, some looked quite meh which is obviously a source issue based on what else I saw. They did show some soccer and hoops, and I noticed nothing objectionable in terms of motion artifacts.
I did see some minor DSE on pans during relatively uniform lighter backgrounds but only on cable, never on any of the BR I watched though perhaps I just didn't watch that kind of scene on BR. It was much less noticeable overall than it was on the 70" Vizio I had, a set which I actually liked given its price. All this said, the Samsung is simply a hands down superior picture than the Vizio. But it should be for 2+X the price...
It's funny I haven't had the 70" Vizio for some weeks now, but the 5" size increase is easily noticeable in my minds eye. This thing feels that much more massive than the 70" ever did.
I do wonder what PQ improvement if any comes with the 7100 or 8000 at this size, though I seriously doubt I would pay for the improvement. Above this price level I think I would only get a full array local dimming set, preferably 4K at that. And as we know current pickins are slim in that category...
One thing I need to prowl the 8000 thread for - there was some discussion there of a dimming feature said to dim only the black bars on 21:9 content, though at the expense of brightness fluctuations during viewing. Not sure what that feature is called but I may give it a look if it exists on the 6400. Otherwise I'm content to enjoy this thing until I decide to get it calibrated.