3D in Eyefinity works, but needs really much power from graphics card, and for FSX especially from CPU. I'm getting currently 15-20 FPS ... (depending of graphics setting and installed addons, of course)
Setup:
3x LG D2343P (passive 3D)
Ergotron stand with long extender bars
HD 7970 GHz
i7 920
For passvied 3D you should sit in a upright position your eyes at the hight of a horizontal line right in the middle of the monitor, becuase of limited vertical angle.
The first is a 2D screenshot, where I try to get maximum FOV thru additional views thru side windows. I think, this is more suited, when your side monitors really are angled in 90° to the side.
The second is a 3D anaglyph screenshot, also availible in
TriDefPhoto-Format. Here I used a wider central view, I feel more confortable with this.