i used a configuration very similar from what you described, but I used 6 projectors in a row.. I did use 2 triple Heads and 2 Catalysts to do it.
So 1 Catalyst and 1 Triple Head gows to 3 projectors, and the same on the second CAT. each one with 2400 x 800. SYNC IDs on the Layers and all went thru OK.
The total of the Image was 4800 x 800, the only issue is you need to make a movie on that configuration.
We toth was too Big, to play on Catalyst, so the guys made a Video of 1600 x 800, and the image inside the Video was squeezed, when I placed in Catalyst, using Aspect Ratio, I did Stretch the image to the above format.
i know is not the best, but work out OK.
Also we used some content making like 3/ 4 layers each time, cloning some etc...
Gian