My understanding is that in SLI, as long as the cards are the same chipset, you can connect them. But I believe you will have to put the slower/lesser card in the number one/primary slot, and the higher card/more memory in the secondary slot. The higher card will clock down to match the one in the primary slot...which essentially you loose it's "full" capability, but in theory you will have SLI. Anyone feel free to correct me on this.