Download the modified Flashrom from here. You MUST use the modded Flashrom, other flashing utilities will not change your pipeline configuration.
Next you will need an unlocked Bios file: Sapphire X800 GTO² | Connect3D X800 GTO.
(only the number of active pipelines has been changed, clock speeds remain the same).
Original, unmodified Bios: Sapphire X800 GTO² | Connect3D X800 GTO
Please note: Many people complain that they get a "file not found" error when trying to flash the Bios under DOS. The problem is that DOS does not know long filenames, so all files are truncated to some funky names like Powerco~1.bin. Either use the dir command, when in DOS, to find out the short filename or rename the file to something shorter while still in Windows.
Use the modified flashrom to flash the Bios to the card. More extensive flashing instructions can be found here. They talk about atiflash - you use the modified flashrom, usage is the same.
After a reboot your card will immediately run at 16 pipelines. No driver installation is necessary.
Verify the number of active pipelines using ATITool. Go to Settings -> Overclocking. The list there shows the number of pipelines the card is running with.
If you want to boost your performance even more, you can overclock the video card. In our tests we could go from the standard clocks of 400 Mhz core and 490 Mhz memory, to the XT PE speeds of 540 Mhz core and 590 MHz memory (actually a bit more).
However, not every card might overclock as well, but all of them should be able to run at the XT speeds of 520 MHz / 540 MHz, probably more on the memory, since it's Samsung 1.6.