I am just wondering, why do you want to run that much water through your overflow?
Unless it is a huge tank I would run a much smaller overflow rate through your sump and hook a big pump like that to a closed loop or something. Otherwise you will have a veritable water fall for an overflow, and a torrent in your sump.
I have even though of toning down my return pump which puts 750GPH at the head into my 150G tank.
JMO.
