I think it has to do with draw calls, the only advantage which has been shown for DX12 is its higher draw call rate, so if you create a scenario where the number of calls would higher then the DX11 limit, you would see a big FPS increase.
I would say the Sony is the best, but Sony's new lineup should be around the corner and all of there 4K tv's will have Android TV built into them. http://www.sony.co.uk/electronics/bravia-tvs-ces