I have one of these monitors and also a 21:9 TV (Philips 58PFL9955H -
http://www.philips.co.uk/c-p/58PFL9955H_12/cinema-219-147-cm-58-inch-full-hd-1080p-digital-tv) - unfortunately they've stopped making them. Its resolution is 2560 x 1080p IIRC.
I would definately go 21:9 again for my TV if/when I make the 4K move - providing they exist of course.
In normal tv viewing I lose a bit off the top and bottom of the pic (e.g. the leader and lap counts on F1 stats) but I can put it back and it stretches the outer 1/4 or so of each side of the picture but keeps the middle in the normal 16:9 ratio. In practice you don't notice anything wrong unless you stare at the edges of the picture of a while.