a 690 = 2 680's on one board that have been nerffed to fit power requirements -> so 2 680's in sli are faster then a single 690. The top line card 580, 680, 780 all can run in four way sli with 4 standalone cards. the 770 and lower cards can only run in 3way, you can add a 4th 770 to the MB but it will not hook up with the other 3 cards that are in sli. the 4th card could only be used as a dedicated physics card, but to be honest would be a waste of money.