Do you remember this news about HD 5550 rebranding? Now AMD goes further and officially (and silently) rebrands Radeon HD 5770 and HD 5750 in Radeon HD 6770 and HD 6750. These new cards will be reserved for OEM in a first time.
HD 6770 packs 800 SP while the HD 6750 packs 720 SP (one SIMD disabled in the HD 6750, one SIMD == 80 SP). Both cards have 128-bit memory bus width, and are OpenGL 4.1 capable.