Running on MAX FFXIV Settings.

AMD Crosshair V Formula-Z
AMD FX-8350 8 Cores
AMD Radeon 7950
16GB G-Skills
Thermaltake 1000W Tough Power
Thermaltake Level 10 GT Case
Windows 8 Pro 64-bit

The FPS are display within FFXIV.

Max FPS:
135.2
Min FPS:
45.8

Remember, cooling is extremely essential to high FPS.
Make sure your system isn't a laptop and that your desktop has sufficient airflow.

I also speculate that your power supplies may be lacking, and unable to push your hardware when it needed most.