Perhaps Jim/Crewzer can (or somebody else) can address how accurately one needs to hold the proper battery voltages (temperature/float) for long battery life---Is it less than 0.1 vdc, or if it is +/- 0.3 vdc OK (I would tend to try and design for the less than 0.1 vdc range).
In another conversation with a fellow HBtr., who has had a solar setup for a few years now. He "says", after trying both types, he now uses 6V golf car batts. Claims in the long run they 1. cost less than 12s. 2 perform better (says their more honest in amp delivery claims). 3. Are tougher and live longer when abused. He claims every system gets "some" abuse and GC batts actually give him less trouble (moe forgiving?). His claim that there are thousands of golf cars using them STILL, this is proof that nothing new can do as good an overal job, or else they wpuld have been phased out by now.
As far as the small tolerences of chargeing the float, IS that realistic or manufacture lawer speak? Can those .1, .3, etc constantly varible rates be done with affordable controllers? Ya'll are keeping your batts that closely controlled? Amazing!