Every CPU has a speed... in which to allow input and output of Ones and Zero's to be looked at and processed... this is Clock Speed and can be measured in time... and thus be calculated as Frequency.
So if you increase that Frequency, you increase the flow of Ones and Zero's...
Now every CPU has electric connections and internal Transistors or switches... that allow, and direct those Ones and zero's, to where ever that CPU is told to send them.
Now... Ones and Zero's are really electrons... and thus current flow pushed by Voltage... if there is resistance to electron flow then you must increase the Voltage.
But... any resistance to current flow has the effect to produce Heat...
The Cpu's, and the transistors in them, are made of Silicon wafers and other elements, that create the internal electrical network and paths for current flow...
But... the purity of the materials used... and exacting process in which they are made... as with anything else... can vary from unit to unit... and electrical resistance in those internal networks can vary... So in other words some require more voltage than others and will produce more heat... to do the same work.
So... basically All CPU's of a certain Model, can be electrically the same design... But due to the Quality and Manufacturing Process... must be run at a different multipler of the CLock Speed ( frequency ), so as not to produce so much heat as to destroy it's self.
Thus... if you can dissipate the Heat produced, in the CPU, more effectively, you can increase the Muliplier or the Frequency of that unit, getting faster Ones and Zero's to be processed... Such as Bigger heatsinks and/or water cooling.
Think of the CPU Multiplier as a coarse adjustment and the Frequency as a Fine adjustment to the CPU processing Speed... and the Voltage must be high enough to keep all those Ones and Zero's ( electrons ) moving at those speeds, without an interruption.