Krazy K,
As you know, I am selling my system to upgrade....great choice on your tank! I ran a closed loop system using only 1 of the two overflows in each corner. I housed a 45 gallon glass tank as my sump. The closed loop system worked as follows:
The return of the left side emptied directly into my sump. I had a generic submersible return pump that was inside of the sump that pumped water back up into the right end of my overflow. I used a 31/2 inch DSB, 3-4 maxi-jet powerheads and around 100 pounds of liverock. I never had a problem with my system. It ran for 2 1/2 years until I recently tore it down. I had 4 160watt VHOS powered by 2 Icecap 430s.