Neither.
At this point I suggest waiting for next-gen which may be here as early as JUNE.
Other:
1. Multi-GPU is always problematic (VRAM isn't currently added so 2x2=2, stutter, may have no support at all..)
2. Next-gen NVidia will add ASync Compute, H.265 and other changes
3. 3x1080p? (Suit yourself, but personally I'd recommend saving up and get a nice GSYNC, 1440p single panel)