Does GPU-Z dump from SPI, from the pci bar, or from 0xC:0000?
SPI is not likely, as i REed it from scratch a few years ago, and almost no-one picked up on it.
As for the PCI BAR: ATI, in its infinite wisdom, disabled reading from the PCI BAR through some magic register (that ATI of course did not tell us about), during ASICInit (the main initialization of ATOMBIOS -- which we got to bisect to find this). At least on the R500 and R600, since this card is likely an R(v)7xx it probably still does the same. We ran into this issue as restarting X is a common thing, while reloading a windows display driver without a reboot is notsocommon.
Dumping from the C segment means dumping from a RAM copy of the BIOS, and some VGA BIOSes are known to edit themselves in place.
If GPU-Z does the pci bar routine, then the easiest way is to boot this card as a secondary VGA device and to not initialize any drivers for it.