If your going to use those 120hz screens for some 3d movies or games, then nvidia is 100% the way to go. No questions asked, it's cheaper and easier to set up and get working. Hell I tried the red and blue 3d and all I have to do is press one button and done. It's a bit more time consuming setting up for the better 3d, but just as simple and easy. And when I looked it up a while ago, cheaper too!
If you are going to stick with two screens, you will not need SLI, but if you intend to get another sceen, then obviously SLI is a must.
Now, here comes the iffy part, if you are going to go triple screen, that 470 card is a terrible choice, nowhere near enough Vram, 2gb Vram or more is a MUST per GPU. If you intend to go 3d AND triple screen, then you need two of my cards, GTX 480 3gb, or two GTX 490. Nothing will come close to having the power to run triplescreen with 3d at any decent FPS otherwise or enough Vram to hold all those textures.
So duel screen, two 470 3d or not, will be fine, or single screen gaming it will be fine. Soon as you go triplescreen, the 470 is going to struggle horribly, more from the lack of Vram (Unless you get the 2gb version) than power though. Although the GTX470 2gb should be able to cope well with triplescreen without 3d and give good performance.
Oh and if you think 4gb of Ram is going to be enough when running games on screens like that, expecially when you crank up the settings, your going to be dissapointed. It's not hard to reach 4gb+ Memory usage on my PC playing just one game! And remember it's no good saying, ''oh but its only using 3gb currently'', because the more ram you have the more Win 7 will try to use for itself and applications. And this will speed up everything on your system.
