More than likely any version will work fine, the differences might be very minor to correct particular issues found in a certified use scenario that may vary with O/S versions.
A few more links:
Load the VBIOS from HP into this tool (the *.rom files) and see what clocks are supported
GPU-z can indeed read and backup VBIOS from a GPU under Windows, but not flash.
The HP provided archives enclose nvflash, which is the binary that allows reading and or writing VBIOS to NVIDIA cards, usable under Linux. I believe the caveat is that the NVIDIA driver needs to be unloaded manually perhaps under linux, whereas the same utility under Windows is able to do it automatically. The hpsetup_generic perl script contains the syntax that is used for doing this under Linux.
For flashing under Windows the corresponding nvflash binary is here: BIOS Flashing Downloads | TechPowerUp
Please make sure you can extract the BIOS with nvflash and load it into kepler bios tweaker and it is detected correctly, meaning it’s not garbage to make sure the tool works correctly before attempting to flash a different version… that’s always good advice for any BIOS flashing… read first and make a backup and THEN write.
As far as experience with the nvflash tool, I’ve used it before, the last time being because a part of the VBIOS of a GTX Titan Black somehow got corrupted and I reflashed the original version again to get rid of the message that was output by nvidia-smi saying so. Since you’re not modifying any of the BIOS files, and only flashing you shouldn’t have any issues. Just make sure to read the documentation, I believe running the binary with no flags will print the usage to the terminal in both Linux and Windows with some example usage.
Another thing to look out for, depending on your system configuration if your motherboard has PLX chips or some weird topology is that the PLX chips will show in the nvflash list of cards, needless to say you would not want to pick those as a flash device, and only your K80 GPU1 and GPU2, however they are designated.