I just did some tests with two of my cards, trying to mine for LTC. Followed the Scrypt readme in cgminer and came to the conclusion that mining for BTC is still more profitable
The cards are HD6570 and FD6670. Both peaked with the following settings at 31Kh/s each:
cgminer -T -l 1 --scrypt -I 9 --thread-concurrency 2880 -w 256
Mining Bitcoins, I get 120~130Mh/s from each card.
Following the calculator here:
http://dustcoin.com/miningI get $0.89 per day mining BTC and only $0.31 from LTC.
Now it is time to test my 7970 and 7870 cards...
Interestingly, I get over 82Kh/s mining on CPU (11 threads, 3930K i7, 4.2GHz)
EDIT: I know what my problem was! I underclocked the memory on both cards to 300MHz for BTC mining. Once I clocked them back up, I stared playing with the intensity and thread-concurrency settings.
HD6570 performed best with -I 17 --thread-concurrency 2880 and 900MHz memory clock, giving me the speed at 98Kh/s.
HD6670 performed best with -I 14 --thread-concurrency 2880 and 1000MHz memory clock, giving me the speed at 104Kh/s.
This changes the picture a lot! Profitability rises from $0.31 to $1.03 per day at today's BTC rate.
EDIT 2: This is getting interesting. Yet another of my HD 6670 cards, showed best performance with -I 16 and gave me 115Kh/s
EDIT 3: The story is different for HD 7970 with memory clock set to 1300MHz. The maximum I managed to get out of it is 404 kH/s (-I 20 --thread-concurrency 8192). This is currently less profitable than mining BTC with the same card @ 650MH/s ($4.88 per day in BTC vs. $4.01 in LTC)