I haven't crashed yet, but I get artifacts in games at these same settings. Could it be a break-in period or is it because I overclocked it all the way instead of step by step in the beginning? I've heard that if you increase your clock bit by bit, it's more stable than going directly to your final overclock.
Stable mining != stable gaming with no artifacts. Try adding a little voltage and or fan speed and see if the artifacts go away.