well that depends on the resolution of your monitors, your in-game graphics settings, and your expectations in regards to framerate. If you are on 3x1080p monitors and want to play with higher settings and smooth FPS gameplay on all 3, get the 780ti. If you want super crystal clear high/ultra settings and smooth FPS then SLI those babies. I am going to SLI the 780ti ACX SC real soon. I'm going for 3D surround though.
In any case, I think the 780ti acx sc is better. That's just my opinion though, I'm no expert.