Sapphire HD6670 Ultimate, HD6750 & HD6770
 

The Sapphire HD6670 Ultimate was able to give me a maximum clock of 870 MHz on the GPU core and 1140 MHz on the memory core, the Sapphire HD6750 was able to hit a maximum of 840 MHz on the GPU clock and the memory clock was a maximum of 1340 MHz. Finally the HD6770 had a maximum GPU Core clock of 960 MHz and 1320 MHz on the memory clock.

http://www.overclockersclub.com/revi...hd6750_hd6770/