I just wanted to add my BTC0.02. As it has been mentioned, for those new to this, you must work through the settings on your own. I have two (supposedly) identical 7970s and they can't operate at the same clocks, but get nearly the same rates.
I have 2x Gigabyte 7970 OC edition, model GV-R797OC-3GD. One at 1054/1500, the other at 1070/1500. For both, --thread-concurrency=8192, -g2, and -I13 (cgminer 2.11.3, ubuntu 12.10, Catalyst 13.1 and SDK 2.8 ). I'm getting 745 kHash/s and 750 kHash/s, respectively. These two cards do seem to be different, as the first is locked at 1.170V and the second at 1.110V. Well, they might not be voltage locked, but cgminer isn't able to change voltages.
Again, these settings probably won't work (exactly) for you, but they might be a good staring place as they aren't too aggressive.
The main point of my post is to say that -g2 should be tried on the poorly performing 7970s, also with lower thread concurrencies. No matter what I do, I can't get either of my 7970s above 600 khps when attempting -g1 and high thread concurrencies. On any version of cgminer that I've used, these settings produce nearly the exact same results.
(edited for spelling)
yeah of course. The clocks card can achieve are extremely variable factor, but I hold my point that in general, same clock/ clock ratio will often deliver similar results
I can't really agree or disagree (though my apologies for sounding as though I did disagree). I suspect that your statement holds for same manufacturer/model cards, but not necessarily between manufacturers, even in the same series.
While this is a limited sample size, I also have an MSI Twin Frozr 7950 and an XFX Double D? 7950. The XFX can do 1150/1750 for 680 khps and the MSI goes unstable at any memclocks past 1500. My best settings with the MSI are 1080/1500 for 625 khps.