So I went with 6v for longevity and deep discharge ability. Doesn't hurt that even these reduced size batteries still kick out 200ah, so same capacity as good group 27's.
Discharge rate isn't an issue unless your inverter is trying to kick start an air conditioner and Max charge rate is 54a on these.
Size wise, these are the smallest 200ah or greater I could find. Most GC batteries are over 10" tall, these are less than 9" tall with flush posts. And 12" long, many are longer. Fit perfect with no slop in my battery tray with about an inch of overhead clearance. GC batteries wouldn't fit in my battery compartment without removing the sliding tray.
And they're AGM.