Shouldn't it not work this way?
It seems that temps (and energy consumption) rise gradually with clock speed, but virtually exponentially with voltage.
Couldn't you get yourself in a situation where you simply have the voltage too high, and there'd be a little more room for clock speed if you backed it down a bit more?
It seems your method would require another step, where you decrease the voltage a little after you've achieved what you thought was your best overclock, then attempt to inch it forward a bit more.
I'm an imprecise and impatient overclocker, I'll admit it.