[citation][nom]SuperVeloce[/nom]84-inch? why not smaller? Is pixel density a problem? Sounds like four 42inch 1080p panels glued together .140cm is about the largest TV for home, anything else is for cinemas xD[/citation]
EVen at that size (84 inches) you have to sit 1.65 meters from it to not lose the full 4k-experience (longer away and the pixels will blend into each other). So, for the normal 3 meters tv-vewing distance it is way to small!
The benefit is that you now will be able to watch 1080 at about 3 meters distance (or thereabout, think it was even 3.5 meters), wtihout losing any visual acuity. As it is now a 42 inch 1080p tv have same same pixel density as a 84 inch 4k tv and to fully get the benfit of 1080p you have to sit at 1.65 meters for a 42 incher (which you can enjoy normally with a 84 incher).
Problem is, that there is still a lot of lowres sd-content out there. Terestrial channels, cable, websteraming and so on will look just terrible on such a big screen.