Those cards won't last long at that frequency. After a few months I've had them die at speeds above 950.
With the Sapphires by chance? I might want to lower my clock rates on my Sapphires then...
Killed 1 xfx 6870 at around 950 and a sapphire 5830 xtreme at the same speed. I still have the dead sapphire, haven't found the time time RMA it :/