I wanted to adjust the CPU voltage settings to get these as low as possible for each CPU, while maintaining full stability.
 
I'm running at 23x185 (4.255ghz), 19x uncore, DDR3-1850.  I started out at vcore=1.3625v (no vdroop), 1.325v VTT on both processors.  I've since been able to reduce the voltage on one processor, and the VTT on both processors while maintaing stability.
 
CPU0 VCore=1.3625v, VTT=1.30v
CPU1 VCore=1.3375v, VTT=1.30v
 
Beyond the obvious benefits of reducing voltages -- at new settings:
CPU0, delta between idle wall power draw and IBT stress (of only CPU0) is 225W. 
CPU1, delta between idle wall power draw and IBT stress (of only CPU1) is 211W.
 
For my stability testing, I chose to use IntelBurnTest, starting at Standard, and then working up to very high, extreme.  However, the approach documented below should work well for most stability testing tools -- assuming the tests don't mess with the affinity.  Folding_at_home should be possible to test in this manner as well (eg: in conjunction with -smp 12 / -smp 8).
 
Step 1
Fire up Eleet, since you'll want to use this for lowering/tweaking voltage settings -- one processor at a time.
 
 
Step 2
Fire up one copy of Intel Burntest and select the number of threads corresponding to one physical processor (typically 12 or 8).  Move this copy to the left of the eleet window.  Now, fire up windows task manager, select the processes tab, and right click on the IntelBurnTest image, Set Affinity, uncheck All Processors, and then select every processor on Numa Node 0.  That should be half of the total visible processors/threads.  If you have disabled NUMA, just select the first half of the processors.

 
 
Step 3
Fire up another copy of Intel Burntest and select the number of threads corresponding to one physical processor (typically 12 or 8).  Move this copy to the right of the eleet window.  Now, fire up windows task manager, select the processes tab, and right click on the (new) IntelBurnTest image, Set Affinity, uncheck All Processors, and then select every processor on Numa Node 1.  That should be half of the total visible processors/threads.  If you have disabled NUMA, just select the last half of the processors.

 
 
You should now have something that looks like the below.

 
 
Start by running the copy of intel burntest on the left of the eleet window, and then try lowering the CPU1 Vcore while re-testing and maintaining stability.  Once you are happy with those results, move onto running the copy of intel burntest on the right side of the eleet window, and then try lowering the CPU0 Vcore, etc.  After both are verified as being stability individually, run both instances of Intel Burntest, and you can also move onto moving an instance with 32 threads (given there is no 24 thread option).
 
Here's an overlay of some of the relevant voltage, temperature, and NUMA labels, since there is some inconsistency in what constitutes processor 0 and processor 1 depending on where you look.

 
I'm interested to hear results others see.  I was pretty surprised by the difference in vcore between the two processors.  I also measured the voltage using the pads on the motherboard:
vcore0 1.36v vtt0 1.336v -- measured.   vcore0 set to 1.3625v, vtt=1.30v in bios.
vcore1 1.332v vtt1 1.315v -- measured.   vcore1 set to 1.3375v, vtt=1.30v in bios.
 
CPU0 VCore=1.3625v, VTT=1.30v
CPU1 VCore=1.3375v, VTT=1.30v 
  
  
 

I measured with the new/final results.  The only value that was a little suprising was the vtt0 value being a fair amount higher than set.
 

may i be worthy

Again, great stuff, I was going to try this but never got around to it.

Glad you also found that CPU0 as marked in documentation and on the motherboard is actually CPU1 in all software reported utilties. What a PITA.

But what is exciting is that you have been able to reduce the voltage on the hottest CPU - win win!

Just to be sure, when you measured the vcore - what was the input in the bios at the time - your starting point of 1.3625v each? or your final result of 1.3625v and 1.3375v?

Excellent info safield -- Will have to give this a try myself.

I wanted to use your process, but cant set the "affinity" from the IBT process in task manager (Win7).  I can see the list with the "affinity" selection when I right-click the process.  But when I select "affinity" I get a pop-up window that says "access is denied".  Is there something I need to do somewhere to get around that problem?  I'm running IBT version 2.50.
 
Rick

I was not running IBT as Admin when I had the issue with setting affinity, but I also tried running IBT as Admin and had the same issue.  You gave me something new to try (clicking on "Show processes from all users"), so I gave that a try, then tried to set the affinity and it works now.  I don't know what that did, but it worked.  When I go back and try the 3.8G OC again, I'll use your process to see how each CPU performs and also to see if I can narrow down that horrible squeal if it happens again.
 
Thanks for the help,
 
Rick