I have two 7870's, and I can't get them past 300 kHash mining litecoin.
using a guiminer script, with  -Thread concurrency 8192  -worksize 256  -Vect 1 -intensity 12  -gputhread 1  , I get around 290khs.

Using cgminer With settings of
"
setx GPU_MAX_ALLOC_PERCENT 100
SET GPU_USE_SYNC_OBJECTS 1

cgminer --scrypt -o pool:port-u user -p password
--shaders 1280 --intensity 13 --worksize 256 -g 1 --lg 2 -thread-concurrency 8192"

 I get about 40. I have tried changing the various values, but nothing seems works..