On an fx5, the water enters the canister at the top and flows down the outside, and then is pulled up through the center, leaving the finer mech last, which would cause lack of flow. Anyone who has had a canister will tell you the flow slows down, and faster w finer mech. The pump in a sump never loses flow regardless of how clogged or dirty the filter sock or drip tray, and if the bio ever never needs rinsed it's minimal co après to the maintanence of a canister
In any case, the fx5 will do the job on this tank but anyone w experience building a sump will tell you that sumps are always a better option due to their larger space for media, flexibility for media, cost and ease of maintanence