For me 13.1 has been faster than 13.3 and 13.4..
Cat13.1 7970 @ 1030 / 1250MHz gets me 720 kHash and 13.3+ 685 kHash
I would like to see your magic formula for 720 on 7970 with core 1030 and memory 1250, this doesn't make any sense .
can you post a Picture here to see these settings , if what you are saying is true this means that we are all doing it the wrong way, or somehow you have some good luck or a magic card .