Could you explain/elaborate porfavor?
You certainly aren't running out of vram or considering maxing out your gpu if you have a card that good, and nvidia's had pretty consistant driver issues with ffxi for the last 3-4 generations. Unless you really really need the default mouse cursor, it's a solid improvement to be using dgvoodoo(shift more load to your super nice gpu, uses more streamlined functions, and option of adding in resharper for a more noticable graphical improvement.. if you do have nvidia crashes it's likely to fix them).
If it were a 5 year old piece of ***card, there'd be more of a give and take since the added GPU load may not actually improve performance. That said, in almost all cases dgvoodoo is still worth having imo.