Iria

"For the overclocking tests I used the Catalyst Control Center to bump up the core and memory speeds a few megahertz at a time until it became unstable and unable to complete a benchmark. Unlike the HD 4850, I could not get as much of an increase out of the RV770 core on the HD 4870. I was only able to get a 30MHz increase, topping out at 780MHz. However, for the memory I was able to get a lot more actually, a 175MHz increase (350MHz effective), bringing it to 1075MHz (2150MHz effective) which is a very good overclock for video card memory. Since this is GDDR5, I did not know what to expect but I am pleased with that bump in computing power. So how will this overclock handle, and will it make a difference since the GPU could only be raised a little? To find out, I will be running the overclocking tests at the speeds of 780/1075MHz. I also noticed that when overclocked even this little bit, the load temperatures peaked and stayed around 86 degrees Celsius."
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Source: OCC