A:Answer The KS8000 is rated as premium HDR (high dynamic range). That means that it can achieve a peak luminance (brightness) of 1000 nits or more. It also supports a WCG (wide color gamut). It has a native 120 Hz frame rate. Basically, the KS8000 is the low end of the SUHD high end models.
The KU7000 is more of an entry level HDR set. It has a slightly wider color gamut than a KU6300. It has a native 60 Hz frame rate. Its peak luminance is about 300 nits. (Not bad, but not "premium".)
If you watch a lot of movies at 24 FPS, the KS8000 gives a judder free image (120 Hz = 24 Hz X5, no "pulldown" is needed). If you want to buy a UHD Blu Ray player to watch 4k movies, get the KS8000.
You can compare models at rtings.com. Their reviews should be taken with some skepticism, but they are a good resource.