I'm no overflow expert, heck I don't even know what a herbie is.
What I can say about nano circulation is consider the rebounds. Maximize your total tank circulation by aiming the returns and powerheads into the corners or sides of the tank for a rebound effect. Because all four sides of a tank are never more than 24 inches from each other you can bounce the flow from one return almost completely back to where it started creating a nice rolling action of flow.
Imagine a powerhead mounted at the front of the tank(1) mid way down aimed up towards the back wall. The water flows across full length of tank and creates nice surface agitation as it hits high the back of the tank(2) and rebounds again into front corner (3) for more surface agitation and finally washes down the front of the tank(4) back towards the powerhead. A nice loop with just one stream.
Koralia Nanos are great, low wattage and thus low heat for maximum thrust.