Ideally, in a perfect situation, everything should work flawlessly. That rarely happens with computers due to all the different software, drivers and hardware that come in so many configurations.
I had a GPU overclock work well on everything - benchmarks, games, testing. No issues.....that was until I picked up a new game a few months down the road. I tried multiple drivers, but it always resulted in the same thing; the new game would throw a few artifacts, hang and crash. I lowered the overclock and the crashes stopped.
If the benchmark is the only thing giving you artifacts and it doesn't happen anywhere else, I wouldn't really concern myself with it. Seeing as though the card is most likely fairly new, perhaps an email to ASUS with...