cgminer settings [ ati / amd radeon HD6870 GPU ] scrypt
Optimum hash rate depends not just on the parameters sent to cgminer but also on how was this program compiled, if it's 32bits/64bits, and the OS configuration.

The best results I've seen are with Gentoo Linux - as you may know, with this distro you first stablish your specific hardware configuration and then compile everything from code, thus optimizing all our software for the hardware you have to extract the most value off of it.

Something you do can do without going the esoteric route of OS tweaking, you could try modifying the GPU's mem clock as well as (slightly) overclocking. Usually, once you hit the point of diminishing returns with the intensity, thread-concurrency and work unit those are the next values to tweak.

If you haven't read the "README" file from Con Kolivas himself, when discussing Litecoin he delineates an optimizing algorithm in which you first find a sweat spot with intensity, then with another value, then another... finally going to mem clock and overclocking, he says you'll extract the best performance that way - such approach is valid for all scrypt-based coins.