What graphics cards are you using? Powering 3x1080p at 120Hz can be tricky.
I personally would say Samsung S27A950D screen, has DVI that is capable of 120Hz, which the 750D model does not. It also has DP, I think you should be covered for both nV and AMD hardware in that case. However, if AMD hardware would cause tearing, I cannot say.
I think personally 3 projects would be a more seemless experience, no bezels to get in the way etc.
Two of Nvidia GTX480. With one 1080p projector FPS all time above 150-200.
I've already tryed 3 projectors setup with curved screen with NTHUsim software but it is only for games not for windows and with curved screen it was very bad with browsing and etc. That's why I'm using flat screen for my projector or wall :)
What you think about plazma or led tv 46-55''? I'm worry about input lag.