Well I would "do it right and do it once...".
Get two e1501's, yes costs a lot more, your can always turn the flow down if too much, and as the filter "ages" and gets dirty the flow will reduce anyway. No need to fiddle with spray bar holes, one 1501 per 1/2 of tank, job done.
The e1501 manual states the 1400litres/hour is the pump, when filter is filled with clean media as supplied will be 800-900litres/hour obviously dropping as media gets dirty.
or
Get two 900's and a power head to get increased circulation ?