I want to buy a second 8800GT and put it in SLI with my current one, but I've seen some cards that say "SLI-READY" on them, and others that don't. What's that mean? So the cards that don't have it are not able to be put in SLI? What if I have one card that is "SLI-READY" and one that isn't, can I put them in SLI?