Ok,im trying to decide on which pump to go with. A sicce 4.0 or sicce 5.0 for my 180 dual overflow aqueon tank. At 5ft of head Im looking at about 750-800 gph with the 4.0 and about 1000 gph with the 5.0. Would the 4.0 be better to allow slower movement over the biological media in the dual...