So, I got a 65" KS8000 thanks to an EPP invite from a generous forum member here, and it has absolutely blown me away.
I'm replacing a 12 year old 42" Westinghouse, and this is a revolutionary upgrade. The black levels are as deep as it gets, even after seeing the OLEDs in Best Buy (I do have bias lighting behind the set, but I've been very pleasantly surprised after hearing complaints about the set not having local dimming), the colors pop, and the set gets bright enough to have to squint.
I've read the entire threads on AVSForum for the KS8000 and for the P-Series Vizios, so I've been VERY aware of the many potential shortcomings of the sets, and I've been pretty worried all the way up until actually turning on the new TV, so it's been a huge relief to be so happy with the new set (no blooming, light leaking, or uneven backlighting).
Luckily, gaming feels great, too (Battlefield 1, Titanfall 2, Uncharted 4), with minimal lag and not really any judder (maybe it's just so much better than my old TV). I like that the old PS4 can do HDR even if it can't do 4K, and I've sold my XBox One so I can buy a One S on Black Friday and get the UHD player.
I don't have cable, so I can't speak to that, but Netflix, Amazon, YouTube, etc have been fantastic both in 4K HDR and regular HD. I've managed to blow away my friends and family with the various 4K demos, and now they're asking about invites to the EPP program (unfortunately, it looks like I can't give out invites with my once-removed account).
If you can find an EPP invite, this set is a pretty great value.