Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
Going by my experience nVidia cards work in SLI without any hitch out-of-the-box (never tested it on 6xx series though by myself), but AMD CF has some issues which AMD needs to take care of with their drivers. Take case of Far Cry 3 - I'm using HD7950 in crossfire and experience...