I play at standard settings with two GTX580s. At times I can hear the fans on the cards start screaming while running XIV (mostly during cutscenes). I think Sath has the right of it by saying the game does not take full advantage of SLI.

However, I do notice that having the Nvidia settings override the game settings for stuff like AA and AO, it does make things run a lot smoother, and the cards complain about the heat less.