120hz on a new Samsung 8000 4k TV

[cellardoord]

Hello, new here, but i've been interested in high frame rates for a while now.

I had a Seiki 4k 39" which had 4k30fps and I enabled 1080p120fps. It was nice to have both high resolution and high frame rate - but the caveat was that I couldn't have both. At 1080p120fps (which was enabled via a custom firmware) had a slightly wonky picture that kinda moved around even with a static screen. At 4k30fps - well 30fps made my computer feel slow and video choppy and I couldn't view anything 60fps let alone 120fps.

So in my quest for a new monitor I wanted to make sure I could have both high frame rates and high resolution, but I also needed a larger screen since it would double as a monitor and a tv - and I actually could use the screen real-estate.

This led me to the Samsung 8000 (UN55KS8000) series 55" SUHD tv.

55" is a little big for a monitor but I specifically chose this model because it has native 120hz and it was the smallest available in the 8000 series - for which the "motion rating" is one of the key differences.

I understand that the "motion rating" of 120 and 240 are not the hz and refer to 'effective' while the native is the actual # -
This UN55KS8000 has an advertised native refresh rate of 120hz (240 motion rate) but after getting it hooked up to my Nvidia 970 I am unable to get it to run at 120 at any resolution. When selecting a custom resolution and then inputting 120, it passes the test but then won't show it as a hz to be selected.

I have a new 2.0b HDMI cable and i've tried the different hdmi ports.

Does anyone have any experience or success is getting a 120hrz tv to display 120 on a pc? Does it have to be in game mode, is there something i'm missing?

Is 120hz 4k even possible? I have a Ge-force 1080 i'm waiting to install - is the 1070 graphics card the bottleneck? The HDMI cable?

If it's a 120hz tv that can only do 60fps now - is that something that can be enabled in the future with new hardware hooked up to it? Samsung uses a "one box" - a little box that you plug hdmi's and inputs into - which is suppose to enable future HDMI upgrades since it's separate from the tv (and super convenient)

Can I at least do 120hz at a lower resolution? Can't seem to get that to work either.

If i'm not able to get more than 60fps on this display (now or ever) then I may return it and trade it for one that 'only' does 60hz since they are significantly cheaper even at the same resolution and size. I could then get a different 55"4k60fps (or 50") tv, and an additional 1440p144fps (ish) monitor that also does 3d for the same $ as this tv. Which would be a shame because - wow the picture is really really amazing and the difference between 30fps 4k and 60fps is insane as it is. I'm thinking the "motion rating" technology actually makes it look higher than 60fps - but if they say it's 120hz and that's the main reason I chose it - I would like to make sure i'm able to use it.

Thanks for any help/ advice!

[Chief Blur Buster]

As far as I know, current 4K TV's can only do 120Hz internally via interpolation.
I have not been able to see a mainstream 4K television that could accept a 120Hz signal from external sources (yet).

That said, a number of TVs can do 1080p at 120Hz via an external signal -- sometimes this is undocumented -- see True 120Hz from PC to TV. This can be tricky, and luck-of-draw if the TV specifications do not support it.