I hate to break the news to you, but Surround gaming will only works properly with 3x 285 cards. Here is the link from Nvidia.
http://www.nvidia.com/object/3d-vision-surround-system-requirements.html
They started to make it possible for 2 way SLI for Surround with the 400 series on up.
Not
quite true... according to that chart, Surround is supported on 2-Way SLI on 200, 400, and 500 series cards, and it will work with LCD's or projectors. I had a double-take at it too when I glanced at it the first time, but there is a division line that doesn't extend all the way. If you go to connector types, it lists the setup configuration for 2-way SLI setup on 200, 400, and 500 series cards.