Those big batteries are heavy. No way would I even think about carrying one up a ladder onto my boat or carrying one down to my dinghy and then lifting it from the dinghy onto the boat. Frankly GRP27 and GRP31 batteries are plenty big enough for me. My Allied has 3 GRP 31 batteries (one for starting and two as the house bank). They do the job quite adequately. My power boat has a GRP 27 start battery and a GRP 31 house battery. I can get away with less battery capacity there because that boat has very few electrical gadgets that will be run when the engine is off. The 115 amp alternator will assure that the house battery is fully charged at the end of each days run.

I would much rather have a bank of GRP27 or GRP 31 batteries than a couple of 4Ds or 8Ds, simply because I can easily move the smaller batteries around myself. Of course, if I was paying someone else to move the batteries every time they needed moving it might be a different matter