Saphhire X800Pro turns up with XT core and 1.6ns RAM

[Legionar]

What do you want me to write into a tutorial???

Download the Gigabyte XT Bios, then flash it like this:
gvf11 -p R80X256V_filename.F1

If it won't flash with -p you need to force it:
gvf11 R80X256V_filename.F1 -f

Done!
That's ALL you need to do.

If you don't want to install your card as a Gigabyte XT you might also backup your old bios and flash it over the Gigabyte bios;
this won't disable 16 pipes again, because flashrom doesn't overwrite everything.
Here you go:

Backup BIOS:
flashrom -s 0 backup.bin

Gigabyte XT BIOS:
gvf11 -p R80X256V_filename.F1
or
gvf11 R80X256V_filename.F1 -f

Re-Flash your backup:
flashrom -p 0 backup.bin

Done.
Instead of your backup you're also able to use the Sapphire X800 XT bios, for example.

You need flashrom 2.37 to do this.