I would drop it 1 at a time and use it for a day after every drop to see if there are any issues during the day. If no issuses then drop 1 tomorrow. Its similar as to how u overclock, but ur just undervolting but pretty much the same concept.
There is no setting in Battery Manager for the Processor. I never thought about it from a battery saving stand point, I figured that if you used a lower voltage kernel your phone won't run as hot, which I suppose also translates into battery use.
I took my Droid off the charger at 7:00 am yesterday, when I got up this morning it had 60% still on it.. Pretty good imho, but I didn't use it much either so that's probably why. Phone standby was the #1 battery user.
That's what I thott...if my phone can handle the volts(no bootlooping and overheating) does that mean I can go as low as my phone will let me IE if at .3 ghz I can run on 1 volt without issues it will be fine (I kno 1 volt is ridicoulos but its just an example)