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Can anyone answer this: can a render engine take advantage in any way of grayscale over rgb? In otherwords, can it be triggered into dealing only with shades of black/white and thus process faster? Might seem trivial, but to an animator the saving of a few seconds on a frame can turn out to be significant. I fight for every second.

::::: Opera :::::

If you're using bitmap textures that have RGB color information in them, then forcing the renderer to turn it to greyscale is going to require more processing time, not less.  You can turn a color map to greyscale using shader tricks, but again, it's more process intensive than just rendering out color information.  It may not even be noticable in time per frame however.  If you start with greyscale bitmaps, or shaders without RGB color info, then you're probably saving on RAM because of the smaller memory demand.  But I would think any minimal gain in render time would be lost in preparing a scene to do this anyway.  You are much better off to just render normally, then convert the scene to greyscale in post.  You will also have more control over the end result by doing it in post.  3dsmax has a maxscript that can desaturate your frames right in the renderer, and there's free scripts and plugins that can desaturate based on z-depth, object ID, material ID, whatever you want.  Using them actually adds to render time, but gives you unlimited control, even deeper than processing the frames later on in some post software.

My suggestion?  Render everything in passes.  Max g-buffer allows for some very deep g-buffer pass control for compositing together later.  You can render entirely seperate passes for lighting, shadows, z-depth, atmosphere, diffuse surfaces, blend surfaces, specular, reflections, self-illumination, and even velocity (for adding post effect motion blur).  Check out the render elements in the render dialogue.