I don't know the answer to your question, but as for an approach you can take, why not try a 20% overclock and run stuff like Prime or Intel Burn Test on it to test for stability? Also see if that makes any difference in games.
If you do a slight voltage increase, you probably will be good for at least 33%.
Actually, try Intel Burn Test before any overclocking, just to make sure you have your heatsink properly fitted.
I must have stuffed up the fitting of the stock Intel heat sink coz my CPU was failing the Intel Burn Test and reaching 92degrees.
Once I fitted my Noctura big boy on it, I passed the highest setting possible on the Intel Burn Test and my CPU never got hotter than 54degrees.