Gate and routing delays as a function of voltage and temperature
For submicron technologies the gate and routing delay variability maximum operating frequency of a digital ASIC as a function of voltage and temperature is more complex than in classic CMOS. In particular, there is new effect called "ITD", see this 
academic article


  One of such factors is the Inversed Temperature Dependence (ITD)
  effect 1. When a circuit is operating in low voltage, the
  propagation delay of a cell may decrease as the temperature increases.


So cooling of a processor does not necessarily help.

For exact details you probably need to contact TSMC, look up their white papers, or look for more recent papers from world SEMICON conferences.

Regarding overclocking, these days must be over: modern 22-14 nm processors employ local embedded LDO regulators that might be set constant but different for different CPU blocks, so external supply voltage has little to no effect on overall CPU performance.