A K SKU model allows the end user to select a free CPU multiplier. For the Haswell Pentium range this could mean boosting performance big time allowing to make up for the dual core solution.
We have tested our particular ES model only on air cooling for the article and got it rock stable at 4500MHz 1.415Vcore. Now to be frankly honest for a daily OC setting I would settle for a lower Vcore around the 1.31ish region.
This would have allowed us to be stable around 4400MHz; the problem this time is not the heat output though the extra current that is required to reach a certain stable setting. The sweet spot for our particular CPU would be 4300MHz at 1.25Vcore. For 4400MHz we needed 1.3Vcore and for 4500MHz required a whopping 1.41Vcore.
In SuperPi 32m we see a tremendous boost from the 1300MHz higher running cores versus the stock ones. Compare especially the OC'ed Pentium results versus the i3/5 non K SKU models. In WPrime the Pentium G3258 is back with a vengeance, beating the with hyper threading equipped i3-4130. This is so typical from old school overclocking. The lesser cores you have, the more important any OC becomes.
Similar trend for the Cinebench R10 64 bit results: the Pentium G3258 outperforming the 50% higher priced I3-4130 processor. The overclock unleashes a demon inside this humble Pentium processor. Cinebench R11.5 show the overclocked Pentium to perform as good as the i3-4130 processor. Sadly not even the 1300MHz higher clocks allow it to come anywhere near the Intel quad core models.