i have a lower level 4k tv..
http://www.amazon.com/Seiki-Digital-SE50UY04-50-Inch-120Hz/dp/B00BXF7I9M
i can say i cant tell the difference.. xb1 is not native 4k or 3d.. with that said the xb1 only has a handful of games that play at a native 1080.. 4k tv's may help the processing power because its not pushed to its max so u will have less frame tears.. but i wouldn't call the frame tears a tv issue as much as a developer issue..
upon startup of my xb1 my tv is 900 @60fps.. so 4k on the daskboard is not going to polish it up anymore..
now with say a blue ray or games at 1080 it may look very nice but i wouldnt say its going to look any better than say a higher end full 1080 tv only because its not steping up to 4k ever. or maybe i havnt noticed any difference..
i will say this .. the frame rate drop is not a tv thing... its in game. say bf4 when a building is droping or what not.. a tv s not going to fix that.. those kind of frame rate drops are in game.