Try putting ffxiv on your SSD. Quite honestly putting your OS on an SSD is pointless. You'll get better boot times, but how often do you reboot? Once it's loaded, that's it. The games are that which have the constant read and write. Choppyness most frequently comes from video cards, in cities, from loading every avatar's little model as you run through, while it's trying to load the city's architecture. Once you are stationary does the choppyness stop? If so, that's the hard drive. If not, it's the video card. The 5850 is an ok card, but probably won't get you much above medium to medium-high settings. If you try on high, you will lag to death. Try turning shadows down first to see if that solves the problem.