Most of the video cards I have looked at lately have a good bit of headroom for the enthusiast crowd. I was expecting the HD 4870X2 to offer that same level of overhead for overclocking. The HD 4870X2 gave up a little bit of love, but not as much as I had hoped for - 55MHz on the GPU cores and 50MHz on the GDDR5 memory. Both pretty low numbers when you consider that this video card is an enthusiast-level card. I suspect that heat is the main culprit in limiting the overclocking here. With temperatures in the range of 90+ degrees Celsius, heat is a major concern, and may ultimately be the problem to solve to get more overhead. At 955MHz on the memory, I ended up with large colored blotches on the screen. At 950MHz, the problem disappeared. On the GPU cores, once I got over 805MHz, I was greeted with lockups and reboots. Setting up a profile in the Catalyst Control Center and modifying the XML file for the profile did not help, as it has with the 4850 and 4870 video cards. The fan speed never changed, so I was left with a hot card and no way to cool it down any more than the drivers would allow; as with any piece of hardware, your mileage may vary. Knowing what my limits were on the clock speeds, I decided to see how much the CPU clock speed was impacting performance. So I pulled the Q9450 and put in my trusty QX9770 to get some real clock speed to find out what kind of performance difference the CPU makes. At 400x10, the performance did not let me down. In 3DMark06 at the default 1280x1024 resolution, the combo did not disappoint - 22520 was the score I achieved.



Link: Overclockersclub