Being an electrical engineer, I have got a couple of thoughts on why people
are having success at lower voltage:
When you use higher voltage, you are
increasing the amount of time that it takes a wave to rise and fall.
This has an adverse effect to overclockers because this will cause waveforms
to run together and blurs how the transistors can interpret them.
Lower voltage cuts the rise and fall time. The waves are not rising from
zero to 1.88V and back, but now only to (say) 1.68V. This makes the waveforms
“cleaner” by eliminating distortion.
The higher the voltage and clockspeed, the more the wave appears triangular rather
than square. So while you need higher voltage to overclock (actually
higher current), that higher voltage increases this time constant.
Perhaps the boards that are overclocking so well at lower voltage do so because
they have a higher CURRENT power supply to the chip than other boards.
They do not require higher voltage because they can push enough current at a lower voltage.
(Ed. note: I’ve asked a few questions, and will update this when I get additional