Also too, I have 460 1gb edition that I overclock and have never experienced any issues, at all. The issues skold is having have really nothing to do with what the OP is going through. AMD cards and Nvida cards are two seperate animals, and not only the achitecture is different, but also the driver structure. AMD cards do not play nice with XIV cuz the game was made to be optimized for nvidia cards.....look at the benchmark for example...huge Nvidia tag as soon as you launch it.

For OP: Do you have any issues with any other games? Have you tried a stress testing program like furmark to stress the gpu and see if it artifacts under load? You could also attempt to play around with slightly older drivers, incase there is a bug with your particiular model and your current driver. Hope this helps!