I am planning a new cell that can handle 50 amps at 12 volts (not 13.8). What power density is good so the cell will not deteriorate?

If I build it with 6x6 plates (reactive area of 5.5x5.5) than if it is configured as

-NNNN+NNNN-NNNN+NNNN-

I could run it at 50 amps with a power density of .5 watts per square inch. Is .5 a good power density? If not, what is?