Mike:
your points are well taken, but
one needs to factor in fuel costs into the charging calculations
if you have nearly free fuel, then i probably makes sense to go with the 20% DOD and burn more fuel
to extend the life of your batteries,
if however one is purchasing pump diesel costs shift
then it makes more sense to go to the 50-80 regime and run more amps ,, for a much shorter period
over the lifespan of the batteries fuel cost can be twice or three times the first cost of the batteries otherwise
it all depends on what one wants to do, and what fuels are available.
i have seen installations that will burn many thousands of dollars in fuel in order to extend the lifespan of their $3000 dollar battery bank
for instance, one needs to carefully run the numbers and not get into the trap of trying to extend a 3thousand dollar battery investment by 50%
(a 1500 dollar gain) if he burns 2 or 3 thousand dollars of extra fuel to get there.
generally speaking anyone that has to purchase diesel will find false econcomy trying to short cycle their batteries in order to extend their useful life.
if you gotta buy diesel the 50/80 regime works out to be the most efficient in real dollars factoring fuel burned vs battery life.
another but...
in order to properly charge at the 50/80 regime one needs a fairly sizeable and hell for stout generating capacity to get 25% into a 1000amp/hr bank
a 280amp alternator is just not going to live trying to meet the 250amp requirment, it likely won't live the first charge cycle unless it has a controller that
monitors the alternator temp and cuts it back as it overheats,,, but then again when you cut back you run much longer.
lots to consider
bob g