Hard Mod ASUS RADEON X800Pro to XT
 

Different grades of the R420 appear to be differentiated by different markings to designate the quality grade. In absence of hard information, we have to resort to the hear-say circulating that the xxx.1 cores are fully functional and can be enabled to run in XT-mode, that is with all four pipeline blocks enabled. Enabling the functionality requires a BIOS flash with the -XT binaries AFTER physically reconnecting the cut traces on the package. To give credit where credit is due, we got the idea for this procedure from this article on PCUnleash.

http://www.lostcircuits.com/video/asus_x800/4.shtml