I used the DOS version, not the Windows version. I would probably recommend you do the same, not sure how well I trust Windows.
I used the exact instructions there in that post, and they worked very well for me. Just make sure you flash the BIOSes in the correct order. Master BIOS first, then slave BIOS, then reboot. And if you're going to flash more than one GPU, make sure you reboot in between flashing each card. The instructions did not cover that, and I found out that if you try to do more than one without rebooting you will brick your card. It's recoverable, but you will need an old-school PCI GPU to recover it.
I used the exact instructions there in that post, and they worked very well for me. Just make sure you flash the BIOSes in the correct order. Master BIOS first, then slave BIOS, then reboot. And if you're going to flash more than one GPU, make sure you reboot in between flashing each card. The instructions did not cover that, and I found out that if you try to do more than one without rebooting you will brick your card. It's recoverable, but you will need an old-school PCI GPU to recover it.