And to revisit my initial questions:
Return placement - ideal flow pattern for heavily planted tank?
1. Circular (create a circular current)
2. Placed for maximum surface disruption
3. Near the top, or bottom of the tank?
I am thinking pandacory's idea of having one flowing under the overflow box is a good idea, although will require either unattractive or restrictive plumbing. So one return (the lower-rated pump) will be on the end pushing water across the back wall of the tank, under the overflow box.
Guess I still need to do some reading on idea flow patterns for planted tanks.