You have to add some DLL's into the Afterburner folder and make some changes to the .cfg files.

Here's a link that explains how:

http://www.overclock.net/a/getting-started-with-radeon-hd-7970-overclocking

I've been able to get #1 card up to 1250 and #2 up to 1300 using water cooling, over-volting and 3 radiators with dual pumps in push-pull.

This got me up to 700MHash/s and bumped me up to #15 on btcmine's top miners list, up from 45 (and climbing).

http://btcmine.com/toplist/

You can save a little juice by cranking the memory clock down as far as it will go. Memory clock isn't very important for mining since hashing doesn't require as much RAM transfer as gaming.

How to overclock: Bump up the clock a little at a time until it wigs out, then bump up the voltage until it's stable. Keep doing so until adjusting the clock and voltage higher no longer results in a stable rig. Then scale back to the last good configuration.

Watch your temps until they level off.