CrossFire and ATI are not supported by FFXIV afaik. They only seem to support SLI and Nvidia cards. Probably because Nvidia cards have much better architecture than ATI cards have. ATI cards almost always give off problems like this in my experience with them which is why I use only Nvidia now. However, all that aside, I get over 200 fps with a single card on max settings. Crossfire or SLI is not needed.