That's likely about right for the turnover thru the sump but you will probably want more flow in the DT from powerheads. You might want to consult the headloss calculator to get an idea of how much gph you will loose after plumbing and sump location are taken into account.
head loss is when your return pump is rated for lets say 500 gph and by the time it goes threw all the plumbing and turns and loops (not really loops) till it comes out of the nozzle back into the tank. when it reaches the point to where it gets to the tank lets say you have a couple 90 deg elbows and every time your water makes a turn it looses speed. so by the time it is back to the tank you may have 400 gph. you have then lost 100 gph because of lift turns and other variables before it gets to the display tank.