Low overclocked GPU temperature can be a safe illusion especially if you're overclocking the memory as the memory chips do not report their temperatures, you are only getting the GPU temperature.
You could be pushing your memory chips to the door of failure.
Are you talking about the RAM memory or my GPU memory? And if it's my RAM memory, how do I go about checking its performance? I watch my GPU CPU PSU and MOBO but never the RAM.
I'm talking about the memory chips on the graphics card itself, they are not temperature monitored and if they overheat you won't know it until they fail.
Some graphics cards just don't have overclockable memory chips, some have overclockable memory chips that are not fully covered under the heat sink and are not being properly cooled.
Once you reached an artifacting stage in a graphics card you're pushing it too far with your overclocking, unless of course it was artifacting at stock speeds before overclocking then you have a factory bad card.