Try 875/1375. I found that yields ~608 Kh/s. Make sure power limit is @ 20%.
If you're using CGMiner, my settings are:
-I 13 -w 256 --thread concurrency 8192 -g 2
Thanks. That did appear to show just over 600khash, but wasn't submitting any shares. Weird.
GPU usage is right up there at the top. Temps are fine. I am on latest stable drivers, but I did try 12.8 as well. I flashed to the GHZ BIOS, but am back on original. I am now up to 590 khash, and my clocks are 965/1575. At these clocks I would expect much more at -I 20. This card still isn't as fast as the 7950. I really think there is just something about this card.
FYI to get close to or over 700 kh/s, you are going to be looking at RAM clocks in the 1700 to 1800 + territory.
Keep an eye on temps. Sometimes a slight overvolt to the memory can help with stability. I'm running 7970s with Arctic Accelero coolers for this very reason.
At current clocks it should be doing over 600. I expect it to far surpass my 7950, but it cant. Card is borked somehow. Those Accelero coolers are nice though.