are you sure it doesn't have anything to do with ccc? ive had this 30% fan problem on many generations of ati cards and uninstalling ccc always allows me to set fan speed with msi afterburner or some other program. did you try the bios update ?

if bios update doesn't help and removing ccc doesn't help (if you haven't already) as a last resort you can try editing bios fan settings directly using RBE http://www.techpowerup.com/rbe/

back up your original bios, and only attempt screwing with it if you have another video card you can use for display purposes incase you brick your 5970 and need to reflash it