OverclockingTo find the maximum overclock of our card we used a combination of AMD internal overclocking software, ATITool and our benchmarking suite.
The final overclocks of our card are 755 MHz core (12% overclock) and 1251 MHz Memory (13,7% overclock). Both overclocks are amazing and show what RV770 can do when properly cooled. Even though the memory heatsinks look quite tiny they seem to cool the memory good enough for an additional 50 MHz overclock above the memory's specced frequency.
When our overclocks are put in perspective to the reference clocks of the AMD HD 4850 (625/993), the margin becomes even bigger: 21% and 26%.
Even though the memory frequency is quite impressive it is still a good deal slower than the GDDR5 used on the HD 4870. 1251 MHz GDDR3 are equivalent in bandwidth to GDDR5 @ 625 MHz.
AMD's reference design HD 4850s were plagued by high temperature problems and users were worried about their hot cards, even though AMD said that these temperature are perfectly fine for 24/7 operation. Sapphire's Zalman cooler does a great job at lowering the GPU temperatures, but it runs quite loud as we mentioned before.