ASUS Radeon X600 XT Extreme
 

"From our experience with the Radeon X600 XT, we knew that there was a lot of overclocking potential in the GPU. From a stock core clock speed of 500MHz and Memory clock speed of 370MHz, we were able to overclock the core 64MHz and memory 49MHz. These results were what we expected, and it can be said that the ASUS Radeon X600 XT Extreme overclocks to approximately the same speeds as ATI's reference design."

http://www.vr-zone.com/?i=1383&s=1