I'm happy to report that I've finally got reaper running successfully at high speeds with very few stales. I now get 454Kh/s or above on my HD6950 (unlocked to 1536 shaders) with these settings:
In litecoin.conf:
protocol litecoin
worksize 256
aggression 16
threads_per_gpu 4
sharethreads 18
lookup_gap 2
gpu_thread_concurrency 6144
and in reaper.conf:
kernel reaper.cl
save_binaries yes
enable_graceful_shutdown yes
long_polling yes
device 0
mine litecoin
Adding 'device 0' is very important as this stops reaper from mining on CPU and GPU which degrades performance.
Clocks are (stable at):
885MHz (core clock)
1000MHz (mem clock)
Great success.I hope this thread helps those who need it.