I was looking at maybe a faulty BIOS. Thanks for the link. The GPU is new and under probably 48hours use old.
It seems as soon as it gets up to operating temp, whether that's 70'c/100% fan, or 75'c/85% fan for more than two minutes producing more than 600kh/s it throttles and then the screen will blink before it slows right down to a halt hashing at aroun 50-70kh/s. At the same time CGminer stops updating, and after 60 seconds or so declares the GPU sick. If using CGwatcher, it will just restart CGminer over and over.
I'll have a look at that link now.
Thanks again.