The general rule is that the lower the voltage kernel, the better the battery life would be, but you also are giving up performance during heavy loads due to there possibly being not enough voltage at specific CPU load amounts. Higher voltage kernels gives you more performance since it offers more voltages for your hardware to operate, but at the sacrifice of batt life and possible higher heat levels if the load is hagi for extended periods.
In all honesty, even a 800 MHz kernel is plenty fast enough, and even a MV kernel at that clock speed wouldn't use that high of voltages since the speeds are lower... or to have a 1.2GHz kernel innstalled, and ajust it to run lower (1.0 GHz or 800 MHz) during periods when you aren't using apps that require more CPU speed.
BTW... uLV is the lowest and if your Droid operates at full loads well on that voltage, then that kernel would offer you the best batt life...