I have a Z77FTW & 2700K I have OC'ed to 4.7GHz and I am currently running Prime95 Small FFTs. EVGA E-LEET shows my CPU temp at 84.0C but RealTemp shows my cores at 64, 69, 70, 72 my core voltage is 1.375V (these numbers are as I am running Prime95) for 35mins.
 
Should I be worried about the huge variance in temps? Corsair H100i (push pull)?
 

Basically, "CPU Temperature" is a single temperature probe in the CPU but not directly adjacent to any individual core.  It is not highly accurate since it is an overall indication of CPU temperature and not an indication of any individual core.
 
"Core temperature" is calculated by using each core's DTS sensor.  The purpose of the DTS sensor is to trigger the CPU's built-in thermal throttling and thermal shutdown fail-safe features.  The DTS sensor is not designed to indicate core temperature, but can be used to extrapolate a fairly accurate core temperature using programs such as RealTemp.
 
I personally put a lot more faith in core temperature than CPU temperature since CPU temperature is just an advisory item instead of core temperature which is an actual measurement of each core's distance from maximum temperature specification which is actually used for critical tasks.
 
BUT, do not assume that the core temperature you are reading is correct. 
 
More to follow...

I have same as you difference on some cores, I saw that is normal thing and lot people over net have that.
Some people even RMA CPU because 10C difference in idle.
And new sample had even worse difference 12C.
 
Example I saw some shoots on Maximus 4 Extreme Z CPU in AIDA64 show 45-50C during stability test,
Cores show in same time 75-80C. That mean how that temps is not accurate as you say. 

I find and this answer from AIDA64 Developers
 
"CPU" temperature reflects the surface temperature of your processor, measured by the onboard sensor chip built onto your motherboard.
Processor itself has quite a few temperature diodes integrated onto certain parts of the CPU die.
"CPU Package" reflects the average inside temperature of your processor,
"CPU IA Cores" is the average temperature of the processing cores (classic CPU cores) part,
"CPU GT Cores" is the temperature of the HD Graphics IGP (integrated GPU of your processor), while the
"CPU #1 / Core #n" temperatures are the per-core temperatures.
 
AIDA64 is very good software, before was EVEREST.
 
Core i7 and Core 2 processors have 2 different types of temperature session; a CPU case (not computer case) Thermal Diode centered under the Cores and Digital Thermal Sensors located on each Core. The case Thermal Diode measures Tcase (Temperature case), which is CPU temperature, and the Digital Thermal Sensors measure T-junction (Temperature junction), which is Core temperature. Since these sensors measure 2 distinct thermal levels, there is a 5c temperature difference between them, which is Tcase to T-junction Gradient.
Intel provide absolute stipulation for Tcase (CPU temperature), but only fractional stipulation for T-junction (Core temperature), which has caused much confusion and debate in the over clocking community concerning test methods, temperature monitoring utilities and accuracy. The monitoring utilities provided by motherboard manufacturers monitor CPU temperature, while some popular freeware utilities monitor Core temperatures. The most accurate Core temperature monitoring utility available is Real Temp - which has several unique and innovative features, and is recommended for users interested in monitoring Core temperatures only. 
http://www.techfuels.com/overclocking/22124-core-i7-core-2-temperature-guide.html

Sensors on my CPU need serious calibration.
On All cores. I need to see how is best way to do that.
And I still need to find Intel official confirmation about TJMAX for Ivy Bridge 3770k, people say 105C but I need to see that.
On Haswell 4770K I didn't so such big difference between cores for now. But I see big difference on MAX temps and on IB is under full load very close. OK I can say only for what I saw, maybe situation is difference.
I can't wait to cross on flux solder Xeon based Intel Extreme.
I mean for 200$ more you got CPU for support Quad Channel and 2 cores more and flux solder.
And performance under OC are almost as double expensive X CPU.