Well the lower the max the more battery your saving. Its all a matter of whether or not your phone can handle it and still get tasks done quickly
Having the max set higher but a governor that keeps it low will accomplish pretty much the same thing.
If your curious, go into setCPU and look at the pie chart that shows you where your CPU frequencies are throughout the day. Mine is below 422mhz 75+% of the time and hardly any at the max if i'm on smartass. If Im on interactive X my max of 1113 is over 50%.
Be careful with your terminiology here. Voltages refer to undervolting, which is quite different than underclocking