It's a pity you can't add more than one graphics card to a PC. Maybe if you could, say, install two cards and set one as the master and the other as slave. That way you'd have two GPUs working on the graphics. Maybe even dual GPUs on each board. You'd have plenty of power then. Failing that, distribute the processing somehow, so each of several PCs is responsible for a part of the image and one PC brings the parts together as a whole.
Just thoughts
