There was an article on this somewhere i read. 8500s in sli were only equal to something in between an 8600 gt and 8600gts. In short, get a better card than an 8500. I think this might be it:http://www.pcgameshardware.de/?article_id=609324
Its in german but if you click on the 2 thumbnails on the left it shows 8500 sli performance in prey and call of duty 2. In short, its terrible im afraid.