Im currently creating footage for my new AV show which uses a dual projection rig on a 6m screen. In the past when creating 3D scenes of buildings or space scenes I have abusing the IA rules a little to push a little more depth into a scene withought making the scene look too macro-ified ( dont know the correct terminology for this phenomenone so if someone could enlighten me! ). Anyway how far do you think is acceptable for example a CG scene to be pushed. I do not need to keep objects to be kept natural in scale as I am using a lot of primatives which do not need to look scaled normally. What I do need to do is push the boat out on how far I can bring images out from the screen withought causing too many headaches. Advice?

If you want to avoid hurting your viewers you need to avoid making their eyes diverge, ie look apart. So really your limited to a maximum on screen positive disparity of 2.5" (70mm). You could probably push that to 3.5" (90mm) if the audience isn't too close to the screen for short periods as most people will tolerate a degree or so of eye divergence. For a 6m screen that's about 2%.