All three of my cards have been factory overclocked, I have not OCed them past the factory.
You can drop the clocks, raise the clocks, try different models, manufacturers, etc. The artifacting is still there.
It doesn't affect every DX9 game, but it *has* been narrowed down to strictly a driver issue with these DX9 games. You can test it by putting the dlls from older drivers in the same folder as the game exe, which forces it to use those instead of the default driver bundled stuff (this was a popular fix to a lot of Fallout 3 problems, IIRC). Some versions of the drivers are way worse than others, and a lot of people have noticed that it seems to be related to lighting effects/shadows in some way.
I can run FurMark all day long and my card never breaks 75C or reports an error, but games that barely push my GPU over the 40% utilization mark consistently show artifacts.
It's a real issue, it's not a bad card and it's not an unstable OC and it's not heat, we promise
It's notoriously bad in Guild Wars 2, it's not 100% reproducible, but for example if I walk past a lantern and see an artifact nine times out of ten if I attempt to do the same exact thing that caused it i'll see a similar artifact.