I'm a little fuzzy on the exact number, but iirc these stop scaling a little after 1.4v on the core with rare exception.   I remember clearly though that after I reached a certain "threshold" I was peaking, and any push in volts past that point really hampered my scores...  
Most definitely not a "blast and win" chip...  gotta find the sweet spot.  
Might want to try this:  I got that last score by adjusting the vr (VERY carefully) during the bench to control the voltage swing.  I was only on cold air, so when I was at my best voltage for max air clocks the load jump would kill the bench, or if set to hit the peak w/ the load jump My scores would drop too...  But, by setting the vr to the "best" voltages, and then tuning (once again VERY carefully) during the bench, I was able to control the swing.  It takes a little patience, but pays off when you hit it just right...  I have no clue how many times I ran that bench over and over to get that score... should have spent that kind of time on the rest of my gpu's...  
