regarding the idea about reducing textures from 24- to 16-bit, I think it was kupa (fractal/metacr.) who once said that they could even be reduced to 8-bit in some cases. I am guessing that the effect of texture-filtering would be to interpolate the colours in either case, raising the rendered effect back up to 24-bit, so a render with no texture-flitering would look worse (using 8-bit textures) than a render with fast texfiltering (using 8-bit textures).