What settings have you tried with CGMiner?
What Catalyst version?
What OpenCL SDK?e
Maybe that is what I'm missing is OpenCL SDK
let me give that a try
I'm using 2.8 based off a article I found here.
You aren't missing OpenCL as you can't mine without it.
I believe Catalyst 2.8 comes with OpenCL 2.6 which is required for 7xxx series cars but is terrible for 5xxx/6xxx cards. So if you can I would downgrade OpenCL to 2.5 which is what I'm using with my 5xxx series cards. But I understand that downgrading OpenCL is very difficult to do.
This is covered in the CGMiner FAQ section.
Good Luck,
Sam