Unlocked MSI Afterburner dont let me pass the overdrive limit

[sewer]

Hello, i hava an ATI HD 6950 2GB XFX, this card have no switch to use the dual bios, and the overclock is limited to 840 MHz clock and 1325 Memory, i tryed to use the MSI afterburner (changing the .cfg file) and I still can't pass the 840MHz, what can i do?

 

[sewer]

LoL sapphire trixx let me overclock all what i want.