Up that intensity. On my 6990 it peaks around 17, unfortunately my computer is unusable but you can play with it to find an acceptable rate/usability.
Okay very many such thanks guys, you've been wow!
so I'm using cgminer 3.5 and a .bat file to launch it :
cgminer --scrypt -o stratum+tcp://doge.scryptpools.com:3333 -u mylog -p mypass --worksize 256 --lookup-gap 3 --thread-concurrency 8192 -g 2 --intensity 20 --no-submit-stale --queue 2
running at 500kHs
let's play with that mystic thread-concurrency parameter now