Do the cards manifest these symptoms only after warming up, or, immediately at bootup?
are the cards at reference speeds, or 'factory OC' models?
They do it in most, not all but most games. The hanging and artifacts normally only happen after 10-20 minutes of gameplay but it can happen much sooner then that.
There is nothing that really triggers it off. I've monitored temperatures and they are always below 65C with my custom fan speed profile.
Clocks are those of reference cards, no attempt made to overclock them in the past and no chance of it happening in the future.