Having learned the tendencies of voltage over many sets of flooded batteries, and now having a Northstar AGM battery I've cycle hard but recharged properly since day one, I am dang impressed by the AGM's ability to hold higher voltages under load at lower states of charge compared to a larger capacity of 12v marine flooded group 27 and 31 batteries.
I imagine gc-2s and thier dense thick plates struggle even more under higher loads than the 12v flooded marine batteries.
Me thinks people in general put too much faith in the weight and price of Lead when stick and brick loads are tried on wheels.