Currently, to my knowledge, over head sumps are popular in Asia. Currently I've got a 5 gallon acrylic one above my 30w. I wouldn't suggest the horizontal media design you have. Mine is set up like a traditional sump, and a tower on one side for filter floss and sponges for mechanical filtration. If your baffles are all below the exterior walls when a baffle reduces flow to the point of over flow water can simply pass over that baffle. and right beside my outlet, i have an over flow, a hole drilled into the top, with a 90 degree elbow. The emergency over flow is pvc and the end that feeds into the tank is above the water so any splashing is audible. Same emergency overflow is on the mechanical filtration tower, and works very well.