What is the highest clock rate that has been achieved? I find anything above 900MHz causes the hash rate to drop in half even when my temperatures are below 80C. I may be power limited or can I play with the voltages somehow?
If you haven't increased the voltages, you'll probably need to in order to get above 900MHz. You can do that using the tool in the thread gateway posted.
https://bitcointalk.org/index.php?topic=639810.0