That's asking a lot, from both your wallet and the hardware (33% more pixels)
The 1080 would get 43.1 fps (75.6 in SLI) at 4k in Witcher 3 and that's by no means the most demanding of current AAA games.
https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_SLI/18.html
3840 x 2160 x 1 = 8,294,200 pixels
2560 x 1440 x 3 = 11,059,200 pixels
That puts you below 60 fps right outta the gate at 1440p x 3
While it's now possible to game on a IPS screen w/o lag or other issues, those panels remain expensive. Grabbing 3 screens @ 144 Hzm IPS and good enough response / lag times is going to cost you upwards of $2,250. Yes, you could go w/ cheaper monitors but doing that requires giving up IPS, G-Sync / 165 Hz and that's giving up too much to my eyes,
The 1080 Ti will no doubt boost that up and it is expected to drop in 4th Quarter 2016, but I expect cost will be up around $799.
One approach might be grabbing 1 screen and the 1080 TIi (< $1,600) and maybe picking up the other card v/ 2 screens afterwards ... once prices drop a bit.