Originally Posted by Maverickman
You cannot use an 8600 GTS with the GTX 295 as they are two different cards. You can only SLI the same two cards: for example, two 9800 GT cards. They don't have to be the same brand though.
physics does not require sli. and to tho OP: most likly it will slow it down due to the 295 being so much faster.