This was extremely useful for me. Other than M=1555 which was too high (1375 worked great for my Powercolor), everything else was used in cgminer 3.7.2 to increase hash by over 15%. Thanks!
BTW, my GPU is not even Tahiti, but Pitcairn, yet the parameters hold well.
In afterburner, set core to 950 MHz and memory to 1555 MHz
use reaper and this litecoin.conf
host yourpool.com ### Do not add http://!!
port 8344
user username
pass password
protocol litecoin
worksize 256
vectors 1
aggression 20
threads_per_gpu 1
sharethreads 32
lookup_gap 2
gpu_thread_concurrency 18610
Tell me what you get
Try also aggression 18