Other than that, the 'sweet spot', is the lowest voltage possible for your desired clocks.
You'll probably find that (for example), you can do 3.7 or 3.8 @ a reasonably low voltage, with a disproportionate jump in voltage required for 3.9 or 4.0.
So, in that case the 'sweet spot' is probably the lower voltage clocks, stable.
Other than that, the 'sweet spot', is the lowest voltage possible for your desired clocks.
You'll probably find that (for example), you can do 3.7 or 3.8 @ a reasonably low voltage, with a disproportionate jump in voltage required for 3.9 or 4.0.
So, in that case the 'sweet spot' is probably the lower voltage clocks, stable.