Unfortunately I don't have any data to compare 12 vs 24V V drops, as when we had 12V we only had a 1000W inverter and rarely loaded it up.
But according to my calcs, at 24V the wires should only account for 0.3-0.4VDC drop with an 1000W AC load. The remaining drop (0.8-0.9VDC) must come from the 4xGC2 in series at these loads (~50A at 24VDC).
Similarly I calculate that at 12V with the same wires there would be twice that V drop across the wires or 0.6-0.8VDC with a 1000W AC load.
IOW the wattage loss in the wires should be identical at 12 versus 24V. (I did use the same wires when changing from 12V to 24V).
So the question is how does the V drop of batteries behave at 12V versus 24V? If they behave like wire or resistors, then the wattage "loss" should be the same and V drop half? But I dunno ...