7950 has 1792 shader units, so try setting --shaders 1792 and experiment with a thread concurrency that is a multiple of that, i.e. 3584, 7168, 8960 etc. Also try updating to a newer Catalyst driver set. I got better results on Catalyst 13.9 than the old 13.4 or something I had first.
--shaders 1792 --thread-concurrency 7168 --lookup-gap 0 --I 13 --g 2 --w 286
cant set both shaders and threads. if you set the tc it ignores the shaders. if you set only the shaders without the tc if will auto calculate what the tc should be.
--thread-concurrency:
This tunes the optimal size of work that scrypt can do. It is internally tuned
by cgminer to be the highest reasonable multiple of shaders that it can
allocate on your GPU. Ideally it should be a multiple of your shader count.
vliw5 architecture (R5XXX) would be best at 5x shaders, while VLIW4 (R6xxx and
R7xxx) are best at 4x. Setting thread concurrency overrides anything you put
into --shaders and is ultimately a BETTER way to tune performance.
SUMMARY: Spend lots of time finding the highest value that your device likes
and increases hashrate.