firs of all set those things
comand prompt with administrator privilege
setx GPU_USE_SYNC_OBJECTS 1
setx GPU_MAX_ALLOC_PERCENT=100

now for getting 600KH with cgminer and 1100 core and a 7950 on cgminer shortcut
--scrypt --thread-concurrency 24000 --lookup-gap 2 -w 256 -I 20 -g 1

this if you want to use your pc and mining at the same time, but only 525KH
--scrypt --gpu-threads 2 --worksize 256 --thread-concurrency 8192 -I 13