290X Crossfire at 1080p is a waste of time, isn't giving the cards enough work, so Crossfire doesn't scale because of CPU bottlenecks.
1440p VS 1080p isn't the huge leap people sometimes make it out to be, but its certainly al lot better for big displays. You still need AA, but the image is alot clearer, and you don't get thin objects popping in and out existence like you do with 1080p.
I've heard that since there's more headroom for higher framerates, playing a game (such as an FPS) on a 144Hz monitor with no vsync on will make it more difficult to aim because drops in FPS can throw off your aim. Say for example if I were to be playing BF4, running at about 80-90 FPS. Then the framerate goes down to 50 because of an explosion, that would throw off your aim for a bit. On a 60Hz monitor, gameplay would remain smooth as long as I keep getting frames over 60fps. I'm not sure if I'm right or not, I have never owned either types of monitors.
120/144Hz isn't really for the extra framerate, 60FPS 120Hz is a billion times better than 60FPS 60Hz (both without Vsync) because theres pretty much no tearing and alot less input lag.
You can have your cake and eat it if you go with an Xstar or Qnix though. $300, 1440p, Samsung PLS panel, 96Hz, no scaler so no input lag.