most recomend 3-5 times the tank volume go thru your sump with only half passing over you fuge. that would be about a 1000 gph pump at whatever height you are running. one return would go directly to the skimmer the other to the fuge. just be sure to look at the head loss grph to determine which pump actually pumps 1000 gph at the desired height, also longer runs and more fittings all cause fiction loss and you may want to guesstimate and add a 100 or so gph. i have a similar setup with 4 foot head and i use a little giant 2400, i think its pushin somewhere around 12-1400, dunno i can't remeber.