So I got some debugging on a 6990 and found that, of course, it does things differently to the 5970.

I've committed some changes to the git tree which should detect 5970s and 6990s reliably on linux, and mumble mumble something maybe on windows. I have at least one report of success on windows with 5970 already.

You can now also mine with 7970s if you specify the poclbm kernel with -k poclbm, but it will perform poorly so it's not recommended.

Intensity can also be increased beyond 10 now (specifically put there for the 7970s) but it is highly advised against for most cards, where 8-9 is usually best.

All this and more, and I even made an exe for windows (this is not the final new version).

http://ck.kolivas.org/apps/cgminer/temp/cgminer.exe

This is taking longer than I'd hoped for the next release to come out, but there are still some final touches to put to it, and I really want things working well. Alas 7970 support is still woeful for now, but that will change thanks to this: https://bitcointalk.org/index.php?topic=61027.0

Give it a go and report back!