For me, I use 106%,  80c, +38mv as doing +38mv adds around 100+ core clock automatically without even touching the core clocks.
 
Best thing I can suggest to you is to run Unigine Heaven in windowed mode with extreme preset.
 
Then make the camera of Unigine Heaven Pause (By going to the camera and clicking on it and selecting FREE).
 
Now loom at the corner while Unigine Heaven's Camera is not moving.
 
Click on your EVGA Precision and click on DEFAULTS.
 
After that look at the FPS on the top right corner of Unigine Heaven.
 
Then Go set you Power Target to 106%.
Remove the "Linked" thingy in precision.
 
Then Go set temperature target to 80C.
 
After that go to Voltage and click OVERVOLT.
 
Set it to max which is +38mv.
 
You will notice that the core clock in EVGA precision is increased (From GPU to another it vary).
 
Then look at Unigine Heaven and you will see that the FPS is increased by 2~3 FPS (Again this vary from GPU to another).
 
Then go and start increasing your GPU core clock by 15Mhz increments untill you reach the max stable.
 
Also, Sometimes Unigine heaven is not very good thing for GPU stability test so you might wanna check something like 3DMark Firestrike and make sure to select EXTREME before doing the test.
 
I ran Unigine Heaven and 3D Mark Firestrike P and didnt have a crash.
 
But when I ran 3Dmark Firestrike Extreme I had a crash so 3d Mark Extreme is the best way to check for your GPU stability.
 
Hope I helped.
 
Enjoy :)
 
Also, note everything you do is at your OWN risk.
 

 
EDIT: Added a picture.

I would also suggest making up your own custom fan curve so the temps dont exceed the temp target.