For all you crazy scrypt/LTC mining fanatics, I have finally found the reason you cannot set very high thread concurrencies or intensities on 79x0 cards. It shall be fixed in the next version. I'm able to run my 7970s at TCs of 22392 now.
And how much faster is it? :-p
7970 @ 1135/1890, LG 2, TC 22392:
GPU 0: 72.0C 3413RPM | 714.6K/715.7Kh/s | A:0 R:1 HW:0 U:0.00/m I:20
No, the memory speed is not a typo. Ignore the accept/reject ratio; I was trying solo.
EDIT: The code is now in git, and here's a windows build with the changes:
http://ck.kolivas.org/apps/cgminer/temp/cgminer.exe