The answer is no; there isn’t a direct correlation, and for a simpler reason than you might think.
While under/over-volting will have a reasonably direct correlation with the amount of power supplied to your clock circuitry, the clock circuitry only controls how quickly the processor turns over each stage of the pipeline. The rest of the circuitry is on a separate power plane, and that voltage is on an as-needed basis, controlled by an entirely separate subsystem.
{edit: overall, as long as you underclock your GPU (which should be happening automatically anyway, though perhaps not as deeply as you are) the power consumption tradeoffs shouldn’t matter in terms of the temperature.}
