I have got nearly the exact same setup as yourself and mine works fine, so there are no incompatabilities in the hardware.
However, I have got one setting different to yourself and I have a strange feeling that this might solve the artifacting problem for yourself.
In the BIOS, in 'jumperfree configuration', I have manually set my "pci-e frequency" to 103. When overclocking cards, when artifacts appear most people increase their pci-e frequency slightly and then the artifacts disappear. The default pci-e frequency value is 100. However, it is perfectly safe to go up to 120 without any problems and is common practice. Raising the pci-e frequency too much can not kill your card or anything bad like that, if it is set too high and you get stability problems, you can just decrease it again without any detrimental effect.
I recommend that you manually set it to 120 and then check if you still get the artifacting. If the artifacting stops, then you can try lower values for the pci-e freq. Keep lowering the value until you start to get artifacts again, and then I would set the setting manually 2 values above this value to make sure the artifacts dont appear again.
Please post back if it works or not
Good luck