Samsung has the "Cinema Black" option that dims the backlight in the letterbox bars. It's not perfect as the surrounding backlight still leaks into the area, but it does help a fair amount. Of course that's just one small part of the image and it'll still be a far cry from OLED.The perfect blackness of the "black bars" due to the cinematic aspect ratio is also something very special once you finally experience it. I watched a few of the "breathtaking" scenes again on the Samsung, making sure I had it set to its best possible image quality for movies, and it looked like complete garbage... contrast makes a HUGE difference in movies.
Unfortunately it's way too late for me to return the set so I'm just going to have to ride it out with the Samsung for now. I'll have a look at the second generation LG OLEDs and might upgrade if they've fixed the dark vignetting/banding and perhaps improved the input lag (for me the sub-40ms lag of Samsung's PC mode is OK), or I might wait until the other manufacturers get into the OLED game.
I also wish there were some effective way of communicating issues to the people and engineers who are actually implementing all this stuff in the sets. Especially for things that are clearly fixable in firmware like the Smart LED highlight clipping I posted about above. As it is, the only option seems to be to hope that they happen to find and fix the issue themselves or that some reviewers with more clout get into contact with them.