Glitches like that could be caused by a faulty graphics card, faulting RAM, faulting CPU, faulting motherboard, corrupt game data, corrupt DirectX, and/or corrupt Windows data. Do you have problems in any other games? Do you see any error or warning events in the Windows Event Log under application or system? Are you using a single GTX 660? I don't recall if there is a way for the FFXIV client to scan the filesystem for corrupted FFXIV files, but that is worth a shot. Possibly install FFXIV to a separate hard drive and test out that installations for graphical corruption.