I think with head, the OR3500 pushes out just about the same flow as the Mag12 (I think around 150 gph less) but with only about 1/2 the watts. At 4' of head, the Mag puts out about 900 gph, which is just about the upper limit for the slotted overflow. Adding more flow via the return pump won't be practical, IMO, and may actually put the tank close to conditions it could overflow the display. We're talking about the possibility of only a couple hundred GPH max for ~50 watts + increased risk. Not to mention the extra noise. The OR3500 is silent in comparison to a Mag. I'd go with an extra powerhead or put in an over the back closed loop.