Novuake :
23.8% for 1366x768
Close enough.
And it was an estimate to prove a point.
Not sure what point you were trying to make.
The steam survey indicates that about 2/3 of people own displays capable of similar or higher resolutions than what you said most people looking at the R7-260 would get "nowhere near" and the GPU list seems to indicate quite a fair chunk of those people must be driving those displays with something quite a bit worse than the R7-260.
My main display is 1200p and I'm still happy with my old HD5770. Most of the details I have to "give up" to maintain decent frame rates are things I would turn down/off anyway because visual clutter annoys me. That tells me the R7-260 is certainly worth considering at 1080p for people who aren't into (ultra-)competitive FPS, RTS and other similar stuff.