> TR 3970X and TR 3960X.
I believe it's like 2-3 times overkill. 12-core 3900x is more than enough, even 3700x is quite good I suppose.
More important you just can't play HDR content in HDR mode at 120 Hz, because:
1. VLC is limited to 3x FRC rate, so ~72 fps is the max
2. mpv currently can't render in HDR mode so it'll always do 8-bit tone mapping
3. DirectShow players will always loose both precision and dynamic HDR data because of ffdshow
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UPDATE: it turns out that mpv CAN finally render in HDR mode after October 30 commit 
So it's now the best choice for HDR content playback.