See my post: http://forum.square-enix.com/ffxiv/t...=1#post1234692

It is an issue with DirectX 9's poor multithreading support. There is no fix outside of rewriting the game engine specifically with a multithread DX9 rendering pipeline with a good thread synchronization backend or updating AND migrating the engine to DX11, which Squeenix claims should happen sometime next year with the launch of the PS4 version.