I tried the 7950 bios on 3 of my Gigabyte cards, one saw a nice improvement, up to 90+ h/s but it fails after a few minutes. The other two only hash for about a minute before crashing. Even adjusting the clocks up/down made no real difference.

Nice find though, good information!! 

Very Important! Notice the "02" in front of the 99 91 and 77 71 in the example above.  Make very sure that the ROM you are modifying has the "02" before changing with the quoted above.  If you have Elpida memory for GigaByte 280x or possibly even HD 7970 it will report as Elpida with Tahiti Identifier application BUT the actual ROM will have "00" instead of "02" which normally indicates Elpida memory.  If you manually modify your original ROM with the above example in that case you WILL BRICK the card.  Ask me how I know.  Fortunately these cards have switches for alternate BIOSES. whew.

Some people don't seem to realize that ZEC mining puts very different demands on your card than ETH mining.  ETH mining is 100% memory reads, while ZEC mining, depending on the kernel code, can have more writes than reads.  When you modify BIOS straps for ETH mining, you might be using read-write turnaround timing that will cause write errors.  Then when someone gets errors or GPU hanging on ZEC mining, they blame the software when their BIOS mod is the issue.
A BIOS guru (not me) can create custom straps that tune each relevant timing value to their safe limits.
The following product brief shows a few of the parameters for DDR5 RAM.  For full details see a datasheet.
https://www.micron.com/~/media/documents/products/data-sheet/dram/gddr5/4gb_gddr5_sgram_brief.pdf