What's the best hardware to run Unity Game with 4 monitors?

Hi everybody,
we are developing an interactive system and we will throw out with 4 projectors our Unity scene. About 200 low-poly moving entities and 2 to 5 low-poly static meshes, so not too complex.
We need this running on 4 monitors, possibly at 1920x1080 each, so 7680x1080 (or with a vertical setup at 4320x1920).

What is the best hardware for this?
Does anyone have a tested configuration successfully used to run a Unity game on 4 screens?

Many thanks in advance.

note: we are testing (and troubleshooting) on a farly powerful pc with double nvidia 690 now but we are having severe stability issues.

We have almost 2 years of experience now running a single multi-fullHD standalone build on single-machine-multiple-display setups.

The most important rule: Stay away from nvidia cards when multi-display output is envolved. It works extremely unreliable, switches display orders around, takes ages to switch resolutions, and whatnot.

The second most important rule: Also stay away from Matrox TripleHead2Go. It is a nightmare to set up - can easily take a day, because something is not working as intended, or the proprietary software claims the desired mode is unavailable when clearly it is not. And it is a joke that you are supposed to buy hardware for 200 bucks just for the purpose of lying to your Windoze and/or nvidia display management, making it believe you are running a single 5760x1080 screen.

For our production setups, we now switched entirely to AMD/ATI FirePro V7900 (4 direct DP outputs, adapters for HDMI/DVI provided (note: with DP->DVI you might need active adapters when using 3 or 4 displays), or the smaller brother V5xxx (not sure about the number).

It works perfectly, no rendering troubles with Unity even under heavy 3xfullHD load (we don’t really use 4 outputs), the screen setup is so easy little children can figure it out (and it just works), and switching between resolutions is possible even on the fly, with minimal delay and no graphics hiccup.