On the Sapphire cards the best I have been able to get is 950/1425 for 650KHs. I am OK with that as they are drawing little power doing it.
I was pushing the memory up and down trying to get a little more out of them and found nothing better up to 1700mhz on the RAM. On a whim I tried 1220mhz RAM and got exactly 650KHs, weird. That seems to be the best so left them running at 950/1220, wish I could drop the RAM voltage below 1.5v...

This is using CGminer with 2048 shaders, 8192 Thread Concurency and - g2 and intensity 13.