Just saying you don't need a huge flow through your sump if you plan the majority of the your displays flow from your CL. Your return pump can be smaller saving cost, power and reduced noise.
Not sure the proper way to figure CL flow from the RC calculator. Guessing probably something to do with area of outlets (4-3/4" outlets is about the same as 1-1.5") but if you have a CL you have zero vertical head. Suggest a post there (RC).
Might also find some help here, at the very least, lot of pictures.
http://www.oceansmotions.com/forum/