Voltage will vary by chip, but I have seen as low as 1.2 to hit 4.3Ghz. My particularly poor i7-4770k requires about 1.3volts to do 4.3Ghz.
1.3 volts is probably a little too much for a hyper evo 212 to handle, but it should still keep it below 80C or so. At 1.2V I would expect highs around 65C under a full load.
Looks like most people hit around 4.5Ghz with the 4690k