Lower your General Draw Quality to 8.

It may seem counter intuitive, but you will not only get better performance, but the game may even look better. Why? Because you drop your General Draw Quality to 8, and you will be able to raise all your other settings and STILL get a performance increase. (I dropped mine from 10 to 8, increased all my settings to max, including AA to 16x, but left Ambient Occlusion off, and my GPU went from 100% to about 80% usage, and dropped 10 degrees C, plus I gained about 20fps).

After you change your General Draw Quality and play with your settings a bit, then I would recommend re-evaluating what hardware you want to update. CPU, GPU, and HDD, can all affect that playability of FF14, depending on how, and how hard you pushing your system.