For testing, we used synthetic tests Futuremark and 3DMark at default settings; and for gaming, all the details were set to maximum detail settings.
After testing this card at stock settings, we overclocked it using ATI Overdrive option in the ATI Catalyst center. Our overclock was modest due to limitations imposed by ATI Overdrive. We overclocked the graphics processor from reference 800MHz to 857MHz, and the memory from reference 2200MHz to 2360MHz. Of course, you could probably squeeze out even more MHz using different overclocking tools; we've seen the HD 2600 XT cores easily reaching 900MHz.
We used the latest ATI Catalyst 7.10 drivers for our testing, and you can download them from www.ati.amd.com Website. Bear in mind that Sapphire and Club3D cards used as reference in the following tables, were tested with ATI Catalyst 7.8 drivers.
In 3DMark03, HD2600XT didn't show some significant performance increase compared to reference cards. The difference was 1028 points, which means the actual increase was only 7.5%. That confirms the 7 percent overclock.
In 3DMark05 the increase actually shrunk – it was just 3.6%.
Just like the previous tests have shown - overclocking this card won't make a significant impact on the performance. The overclocked card was faster than the reference one by 5.5%.