I have the 3GB 580 GTX cards,and they are not supported BIOS of 70.10.48.00.01 in fermi or nibitor.You can still make changes to fan speed and voltage.
I have changed my BIOS to 1.213 and 30% min fan speed can be done.
You should have the same BIOS on your CARD.If you upload it here I will make the change for you to 30% min.There is always a risk when flashing BIOS.
Save bios in gpu-z I will change it for ya.