Looks Good, I remember when I was using a 920 DO in my now secondary EVGA X58 E760 Rig I have for gaming/general use, But it has an i7-980 in it now.
 
Have you tried to run 3DMark benches at that 4.2GHz OC using your two R7950's?   

Yeah, I've managed to fix a few Graphics Cards in the Past using the "Shake and Bake" Method which obviously as you found out is very particular on maintaining the right temperature/time periods.
 
Good benching scores just running one 7950 at 1150MHz on air and the 920 at 4.189GHz on water cooling.

 I'm thinking for the ram speed you have that you shouldn't need to raise the vtt so much, maybe not at all.( Many people raised that a lot, sort of a crutch, scared to put more vcore.) Which may help your temps a bit.QPI PLL, I believe there is a lot of headroom on this one 1.4 is safe. The big weakness on these chips/boards is the north bridge temps. I used to have "a golden" 920 that did 4.6 or so with the voltage you are using. There's another voltage don't remember what it is called, but the default is 1.8v try lowering it to around 1.6v. There is also another setting, again I don't remember what it is called, but go negative.
 Do these and try lowering your vcore. My money is on you can get the same OC with less vcore and lower temps.

I'll try messing around with the voltages tomorrow. And, the imc sucks on this chip so anything below 150mV vtt is not possible unless I clock my ram down to 1333mhz.
 
 
Both the VRM and NB temps are perfectly acceptable (VRM: below 60c NB: 50-55c. Cooling is a corsair H110 @ max fan speed.
 
I think you're talking about the CPU PLL & ICH VCORE, correct?

Mother Board ( EVGA X58 SLI LE E-757 )                                                        
Drivers ( ? ) 
Bios ( 82 )                                                                                                      
 CPU ( 920 D0 )            
CPU Cooler ( Corsair H110 ) 
Memory ( Samsung M378B5273DH0-CH9 2x4GB ) 
PSU ( EVGA 1300 G2 ) 
GPU ( MSI TFIII HD 7950 ) 
Drivers ( 14.9 )                                                                                                   
Operating System ( Windows 8.1 Pro 64 ) 


Frequency Control 
CPU Clock Ratio ( 21X )                                                                                          
CPU Host Frequency (Mhz) ( 200 )                                                                       
MCH Strap ( Auto ) 
CPU Uncore Frequency (Mhz) ( 3590Mhz { 16X } )                                                 
CPU Clock Skew ( 0 ps ) 
Spread Spectrum ( Disabled ) 
PCIE Frequency (Mhz) ( 100 )

Memory Feature         
Memory Speed ( Standard ) 
Memory Control Setting ( Enabled ) 
Memory Frequency ( 1602Mhz / 2:8 )                                                                 
Channel Interleave Setting ( 6 Way ) 
Rank Interleave Setting ( 4 Way ) 
Memory Low Gap ( 2.5 ) 
tCL Setting ( 9 ) 
tRCD Setting ( 9 ) 
tRP Setting ( 9 ) 
tRAS Setting ( 24 ) 
tRFC Setting ( 128 ) 
Command Rate ( 1t ) 


Voltage Control 
EVGA VDroop Control ( Without VDroop ) 
CPU VCore ( 1.40 )                                                                                                 
CPU VTT Voltage ( +150 ) 
CPU PLL VCore ( 1.80 )   
DIMM Voltage ( 1.50 ) 
DIMM DQ Vref ( +0mV ) 
QPI PLL VCore ( 1.20 ) 
IOH VCore ( 1.20 ) 
IOH/ICH I/O Voltage ( Auto )  
ICH VCore ( 1.10 ) 


CPU Feature 
Intel SpeedStep ( Disabled ) 
Turbo Mode Function ( Enabled ) 
CxE Function ( Disabled ) 
Execute Disable Bit ( Disabled ) 
Virtualization Technology ( Disabled ) 
Intel HT Technology ( Enabled ) 
Active Processor Cores ( All ) 
QPI Control Settings ( Enabled ) 
QPI Link Fast Mode ( Enabled ) 
QPI Frequency Selection ( 4.800 GT/s ) 
OC Recovery ( Disabled ) 
Turbo Performance ( Disabled )  
 
 
I might try updating the bios to see if that helps any.

I dropped the CPU PLL down to 1.725v and upped the QPI PLL to 1.3v. It's doing ok at a vcore of 1.3875v so far, though I haven't done any actual stress testing with it yet, just 3dmark & cinebench.
I also dropped the IOH down to the stock 1.1v

Ok, I managed to drop the vtt to +75mV and the cpu vcore to 1.375v.
I noticed something though, if I lower the cpu pll lower than 1.725v I get a consistent drop in performance. I'll see if bumping up the qpi voltage does anything.

The temps are about 2-4c less on the hottest core.

I am able to achieve 4.3GHz stable using 1.44375v (1.43v measured with multi-meter) & temps don't break 63c on the hottest core when running 3dmark 11.
Performance is worse than 4.2GHz, guess I hit the max for this chip, under water at least.
 
Thanks for all the help awalleyeguy!  
I've learned a lot from this venture, i'll make sure to use this just obtained knowledge to oc my X5650 to the max when it arrives.

awalleyeguy
 Performance dip might be related to memory. 

In what way?

Incorrect timings, incorrect voltage somewhere (ram), something getting to hot, IOH I believe is northbridge voltage. For the most part raising won't do anything (except make it hotter) unless you are going extreme. (LN2, dice) but there is a little room to lower it a bit. BTW unless you are using a IR thermometer there is no temp checking for the north bridge. There are readings that say they are but not really, at least back when I was using the EVGa X 58 759 Classified.  
Once you take the ram out of specs (overclock it) the timings and or voltage may need to be adjusted. When the X58 chipset came out Intel said ram voltage shouldn't be more than .5v higher than VTT. Intel also wanted no ram over 1.5v, but at the time there wasn't hardly any around. 1.65 was the standard and it didn't kill any chips. Point being you should be able to increase you ram voltage and not break anything.

 Not bad. Have you tried bringing that voltage down a bit?

 Yes you can. 2 things you can do 1 turn off HT. 2 In cpu settings you can select number of cores.

When you disable HT you will have to lower some voltages. Don't remember which ones. VTT is one, probably Vcore also. To much voltage can be as bad as not enough. Disabling cores is pretty pointless unless you want to run some single thread bench or something like that.