Disable catalyst from the msconfig, after you have turned-on performance mode.
Use afterburner, with all the advanced options selected, (the ones that unlock all the values and extend values beyond normal driver settings.)
Use the "delete profile" trick to get the lowest clocks you can. (open AB, detect cards, lower memory values, do NOT restart the computer like it asks you to do, turn-off AB, delete profiles, restart AB, detect adjusted values as defaults, adjust lower, turn off AB, delete profiles... eg, repeat until you are down to 35-75 for memory. Then SAVE as profile 1. Then manually edit that profile to ensure the new clock is saved, and LOCK the profile by changing the file to a "read only" file.) Now you just start AB and load those settings you want.
First, you need to "lock voltages"... then "set voltage to one of the 4-profiles" (If you have a card with "locked voltage profiles".) For both core and memory. (Memory is limited to 1.5v 1500mv, I believe.)
Second, you need to adjust power consumption to -20 to +20, depending on the power available... (Not sure how may watts you have, or what wattage cooling you have.)
Third, Reduce memory clock to a stable low. (I can go as low as 35 with my low-power profile. But 75-150 is more stable. Higher clocks require higher voltages and available power in wattage from the system. Unstable = underpowered or just mismatched clock-ticks. EG, 35 might fail, 36 might work due to clock-ticks matching.)
Fourth, work on your core clocks... This is SUPER SENSITIVE... Not every "frequency" is valid, or works... Just like the memory. It is power-dependent and also timing-dependent. 1024 might work, 1025 might cause errors, 1026 might work, 1027-1029 might cause errors, 1030-1032 might work... etc...
Bitcoins are ONLY clock-sensitive. Memory is irrelevant, because commands are delivered directly to the card, not buffered in memory. There is no "work" being done in the memory of the card, other than a few holdings, which are less then 300 per second. (Thus a clock of 0.3mhz would be sufficient, if it could go that low.)
If your memory is stable, and you have enough power left, push the core to a comfortable cooling limit that is no greater than 85c. 75-80c is better. 70-75c is the best you should expect with air-cooling, while running at a max.
With air-cooling, and within my wattage range, I can get up to 712MHs, but it needs a rest every few hours. Running at 680MHs, it can run all day, but I give it a rest to cool the other components and let the core cool. Running at 620MHs, I can go over a week, without worry. (Wattage range is within 1500-watts for 6 cards. Unpopulated system consumes 45Watts. Thus, each card draws about 235-watts at the wall. I run about 1400-1455 watts, staying under load with 6x 7970 cards per MoBo. MY values will not do YOU any good. Each card is unique, even by the same manufacture. Also, all my cards have been properly heat-sinked, unlike stock reference designs, which have poor contact.)
To push it over the 712MHs, you need more fans and/or water-cooling. (Both those add more heat and wattage to cool, defeating the purpose and negating any potential gains.)
However, if you expect the bitcoin to rise in value, then the gains MAY be rewards, as earning low-valued coins now, is better than earning a high-valued coin later, at the lower clocks. However, that is a "risk". One which has multiple losses, if you are wrong, and half as may losses if you are right. (Dead cards, wasted power, additional expenditures from overhead.)