My bog/gravel/plant filter is 26 feet by 4.5 feet by 2.5 feet deep. The first summer it was fed water by a pump that only pushed around 200 gph, old slow pump. The plants started growing great.
Mine is now fed by my pond pump. It is my only filter, the pump is rated at 6500 gph, without discounting head pressure.
That's as big as my actual new pond!!! Got a few days to think about it whilst I knock down the brick work around the pre-formed.