So in theory running at lower speed and lower voltage should be fine, but maybe there are some chips that really need the extra voltage to be stable even at those.
You will want to be running DOCP speeds (or higher) for performance reasons anyway, although given your issues I would verify it is stable before tweaking anything.
You will want to be running DOCP speeds (or higher) for performance reasons anyway, although given your issues I would verify it is stable before tweaking anything.