My own performance can go up or down 10fps during hunts depending on how many of certain roles turn up.
If you have scholars about using sacred soil or bards using flaming arrow, this definitely affects my framerate.
Most recently, my framerate dipped into the teens and i actually had to drop the max object count to minimum to keep it playable, there was that many black mages hitting it with flare it only took half a minute to kill.
Ah, someone just posted this, and it does seem to have a minor impact for my system
http://forum.square-enix.com/ffxiv/t...in-Performance.