Firstly what CPU and motherboard are you using?

My i7 920 CPU has automatic CPU voltage (vcore) and this is standard about 1.13 volts with 21x133 - the 21 is the clock ratio and the 133 is CPU host frequency (could be called QPI/Bclock/bclk).

The CPU actually has a ratio of 20x for each CPU core but one core will run at 21x in turbo mode (or something like that :p) - the i7 CPU has 4 cores. My i7 CPU is therefore 20x133 = 2.66MHz but I have it overclocked to 20x190 = 3.80MHz

Some Bios may not allow you to change these values. I think you can try reducing the clock ratio first and reducing the CPU voltage. I doubt you can do any damage to the CPU by reducing voltage because its designed to work at a higher voltage but you may loose stability as you reduce the voltage. Try using LinX to stress the CPU at 100% useage to test for stability.

I think if you turn on all power saving features you'll automatically underclock the CPU until it needs more power.

I'm no expert so this is just my opinion