I am now running at Core 866 and Memory 1500, getting 610 kh/s per card... Since Memory at 1600 led the card to crash after 1 mins.
No I have 3 cards. And I don't have a cgminer.conf in the directory, I run a bat file.

-I 13 --thread-concurrency 8192 --gpu-engine 866 --gpu-memclock 1500 --auto-fan -w 256 --shaders 2048 -g 2 --lookup-gap 2