I read about this in another thread but didn't want to hijack. People were saying that OCing the memory clocks too high would cause cards running GDDR5 to die, but "too high" isn't detectable.
This is the first I had heard of such a thing and has be a bit worried. I'm running an Asus 670 at 1280 core clock (+140) and 3500 memory clock (+500). I don't notice any artifacting in games, and it doesn't crash. I ran Unigine over and over and its stable.
most of the GDDR5 memory chips are manufactured to operate at speeds well over the speeds that can be achieved by overclocking.I have never seen someone achieve such levels of oc as to damage the memory chips itself.
the effective clock speed of gddr5 memory can reach upto 7ghz...i don't think anyone has reached that levels.