I run a GTX 660 SLI setup and never see over 75% utilization on each GPU. My CPU usage hovers around 80% or more for one core and about 50-60% for the remaining three. I have an i5-3570K @ 4.2GHz. It seems pretty much par for the course that you will see GPU usage discrepancies FFXI using SLI rendering. Many games exhibit this same behavior.