you really don't need two graphics cards. having one ati x850 plat. edition 256mb will effectively soft cap performance on most games. obviously having two will give you better performance, but definitely not on a linear scale, yea?
sli only gives better performance on some games, but ati's system (like sli, but different name, can't remember it off the top of my head) is far better.
:lol: AMD is a processor maker, not a graphics card maker. nVidia's SLi was originally meant to work only with AMD. P.S. SLi is the highest performance you can get.
What SLi does is takes 2 video cards and split it up. The first video card takes the top half of the screen, and the second does the bottom half. It's not really worth it at this point in time, considering a 128mb video card can play any game right now.