I also use the same card on my desktop and it is working fairly fine. But i have heard lots of others, complaining about this. My Card is MSI btw.
Did you recently installed your card? If yes, are you sure you have removed all drivers of your previous card?
Also keep in mind that you should Defragment your hard drive every once in a while, not only for FFXI, but for overall maintenance.
Maybe you should try updating your video card drivers. Also email Square Enix about this. They probably recieved lots of complaints about this, and have a solution.
I actually don't know how they reply technical queries but, I remember, Activision messed with my PC for days, checked my logs, found out every single updates that my Pc needs to run Doom 3 well. Maybe SE Technical Support does this too. Its really helpful and worth trying.