hmm.. very bad indeed. I have Win8.1 installed and no problems since release. All updates installed too... Looks like it's a nasty bug... a reformat is in session although i do hate reformatting because of one software issue. And that you reformatted seems to repeat itself? Wow, maybe an AMD issue with FFXIV graphics coding.

I have and AMD8350 wih a NVidia GTX 580 and 16gb of RAM. As far as I can tell. Smooth as butter for me. No slowdowns or Bluescreens. I fixed all issues related to FFXIV to run by setting my cpu voltage to 1.42... this game seems to use lots of cpu power.

Hope someone can fix this problem for you. Cheers!