If I'd been replacing something that was even semi-functional, I'd have done that... but my my charger was non-functional and my batteries wouldn't hold a charge overnight so something had to give. My biggest power expenses will be the instrument and autohelm and the fridge. Out of the water, I don't think measuring the autohelm would be useful info and the fridge isn't currently functional. My choices were to replace the 27's already in the box, to replace with 31's or move to GC's. The latter makes the most sense from an expected cycles standpoint so that meant I could choose between the 12's and the 6's and I opted for the former because it's simpler albeit possibly the more expensive choice. Good call or bad, it's behind me now.
The charger I'm going with is the ProMariner ProNautic 1250. It's the same device as the Sterling that Maine Sail likes but my local marine electrician is dealer of the ProMariner version. I'm replacing a Xantrex Truecharge2 40 A that went belly up way too early and I learned during that ordeal that their tech support is pretty awful. I chose the 50A version based on the size of the battery bank and the advice of ProMariner Tech Support.