Díky dobré výtěžnosti zvyšuje ATI oficiální frekvenci X1800XT:

625MHz -> 650MHz (jádro)
750MHz -> 775(1550)MHz (paměť)

This ATi document - ATi RADEON ‘X1800 XT OC support’ - effectively advises that due to better than expected yields of its X1800 XT ASIC, ATi is guaranteeing that the clock frequencies can be raised from the original reference design VPU core frequency of 625MHz to 650MHz, and that it’s recommending that AIB partners wishing to ship products at this core frequency, should also increase the video memory clock by 25MHz from 750MHz to 775MHz.
http://www.hexus.net/content/item.php?item=3902