OP what CPU are you using? I know that 1.0 isnt that greatly optimized to begin with, but you should see SOME noticable improvement in game with an SLI setup.....thats also assuming SLI is setup and configured properly in Nvidia Control Panel and you are using fullscreen mode on 1.0. Somethings leading me to believe you have a bottleneck....Also too, what is your cpu utilization % in task manager when ffxiv is running?

Also too, as far as I've understood it, ARR will be much friendlier to SLI/CF setups, so def no worries there.