use the carrara 6 pro renderer for exported pz3 files (poser scenes).
those render settings are about as low as one can go.  maybe ray-traced shadows
would be quicker than ambient occlusion, unless forced to use IBL, which is vastly
inferior in FFRender than most other renderers IMVHO.
uncheck "smooth polygons", "remove backfaces" and "displacement maps" if possible.
if stuck with FFRender, reduce all textures to minimum size, delete all unused morphs,
do whatever the others said, but skip the part about virtual memory, as apple has
thoughtfully taken away control of that from typical users.
yes, vram only affects the speed at which preview screens can be manipulated.
apple hasn't yet incorporated the "vram-sharing" module into its OS AFAIK.