nope, it won't go below 40% even when using MSI afterburner....
i haven't tried this - but this is what i think...
i've read somewhere that you can write your own bios to unlock fan speed (ex. non SOC GTX580s are max 80% fan speed).
i reckon this can work the opposite by opening up the lower threshold to 30%
you can do some research in google about it.
