Overclocking Cape Verde
Radeon HD 7000-series GPUs have shown great aptitude for running way past their default specifications. Tempering any enthusiasm before we overclock, know that HD 7770's default core speed is the highest we've ever seen from a reference card.
Catalyst Control Center and any third-party overclocking utility limits the maximum frequencies for the PowerColor HD 7770 to 1,200MHz core and 5,000MHz memory (1,000/4,500MHz default) , while the HD 7750's limited to 900MHz core and 5,000MHz memory (800/4,500MHz default). This behaviour is consistent over three PCs. However, as you will see in a separate review, Sapphire's HD 7770 OC has higher limits. AMD's unable to confirm why this is the case.
Operating at default voltage, we managed to max out the 900/5,000MHz clocks for the HD 7750 and hit 1,150MHz core and 5,000MHz for the HD 7770. There's sufficient reason to believe the memory will run faster, much faster, and this section needs to be revisited once higher limits are exposed for these reference cards. Sapphire's card managed 1,200MHz core and 6,200MHz memory, incidentally.
We've re-graphed Aliens vs. Predator at both resolutions with the two Cape Verde cards overclocked.
What's of note here is the lack of performance increase once the HD 7750's clocks are raised by over 10 percent for both core and memory. We believe this to be a driver issue and are in discussions with AMD over this.
The HD 7770, meanwhile, adds a satisfying dollop of extra grunt with the elevated clocks, though they're nowhere near enough to challenge the HD 6870 or GTX 560 GPUs.
