Soldato
It's definitely possible to write a custom bios that allows the fans to turn off at a certain temperatures. I doubt that gigabyte will release one but I am certain that a 3rd party will do it (like skyn3t).
Also as long as you can flash the original bios back onto the card then the warranty will remain. I returned a rubbish 780 lightning that I flashed Skyn3t's bios onto and reflashed the stock bios back on before return.
Thanks Disco, much appreciated. That's good to hear. I'll also make sure that stock bios can replace any third party bios before i try it