I run everything at ultra settings so full antialiasing etc and although FFXIV ARR is happy to run it, the GPU does sit at 100% usage while doing it. Theres no negative affects of doing so, the display is still fine/frame rate doesnt suffer, just might help to have more bandwidth available in your card for future proofing. I'd guess the GTX770 or 7970 should handle it relatively easily and should still cost around the same as a 670. Although i guess its not necessary to place everything on max.