Best way to Undervolt a i5-3570K and Z77 motherboard

Given the thread on the inaccurate CPU voltage some Asrock Z77 boards are delivering
I figured I would downvolt my Extreme6 and i5-3570K. It's running at stock frequency anyway, and that's probably good enough for me
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I'm not sure the best way to do this. In the bios, I can set the CPU volts to manual, something like 1.040 V for now, and then test for stability. Or how about negative offset?
How about PLL, should that be lowered to something like 1.586 V?
Then leave everything else at default in the bios?

Some Testing Here:
Stock settings::With all auto settings, prime95 running, CPUZ says 1.144 core volts

NEXT::
CPU voltage fixed at 1.040V, PLL set at 1.586V
with prime95, 100% core usage, CPUZ says Core voltage is .984 V, temps at 50C.

Core voltage reported by CPUZ at idle actually goes up to 1.032V, is this what is called Vdroop while under load?

NEXT::

should I leave CPU voltage at offset mode in the bios, and enable a negative offset?

Results with offset mode CPU volts in bios, and a offset of -0.195V, prime 95, CPUZ says voltage is at .968V while under load. Temps about the same, 50C

offset mode CPU volts in bios, and a offset of -0.195V, while at idle, CPUZ says volts are .840..wow, tha sounds low…