Most of the render time was still consumed by P5's tendency to take absurdly long times generating shadow maps. I've discovered that increasing the bucket size will generally help with shadow-map calculations. There's a point of diminishing returns, however, which occurs as you run out of system resources and Poser starts thrashing your hard drive. I'm not certain that using greyscale textures would boost performance. Poser still needs to upsample the textures to 24-bit (or whatever) uncompressed bitmaps before it can start rendering, right?