take a look at GB's forums
As farasI can see there have been some issues with someofthe other SOC cards as well (560s etc ?)
I think personally they are just pushing the factory overclock bounds too far (or are not binning/testing thoroughly enough)-but that may be not correct at all -I don't know
Sucks because the SoC used to be really good cards that actually were cherry picked and not only ran stable at the upper end of what was possible with other cards, with lower power usage and better heat transder out the box but also had 10% or so headroom above that for user clocks. Since the 480 onwards the sorting process seems to have gone out the window