With the DFI nF4, you need to leave VID at Auto in the BIOS or else CnQ cannot drop the voltage. However, you can set VID Special to 104%, 110%, etc. if you need a bit more juice for overclocking. This VID boost will be applied on top of what CnQ does to the voltage. For example, if CnQ drops the base voltage to 1.0V, with 110% you'll see 1.1V instead.
If you are dropping your CPU multiplier in your overclock, you'll need to make sure you set the "max multiplier" or whatever it is called in the BIOS too. This is the maximum that CnQ will use.
For example, I am running my Winchester 3500+ at 240x10. I have VID set to Auto, VID special to 104%, CPU multiplier 10, CPU max multiplier 10, and CnQ works fine. It drops down to 1.0x1.04 volts and 240x5 at idle.
Then again, since I started folding for SPCR it has never dropped down to idle...
QX6700 at 3.0GHz, Ninja SCNJ-1100P, 8800GT, Asus P5K-E, Seasonic S12II-500GB, 2x WD5000AACS, Antec Solo
Opteron 170 at 260x10 w/7000B-Cu, 6800 GT w/VF700-Cu, DFI nF4 Ultra-D w/NB47J, Seasonic S12-500, 2x WD5000AACS suspended, Antec SLK3000B