For me, a single VarioS-6 would be my choice. I've been thinking of flow in a completely different way since we did the BRS/WWC Hybrid series in that, flow in the DT and flow through the sump are completely independent of each other.
This in mind, really all I need a return pump to provide (in terms of flow) is enough turnover through my sump to heat and filter the water multiple times throughout the day. Whereas flow inside the tank for coral metabolic function is solely based on the powerheads and pumps inside the display tank. That said I don't really need a TON of GPH turnover the DC tunable nature of a VarioS-6 means I can tone it down to 2-5X turnover and give my filtration enough contact time to work effectively and efficiently.
This really is summed up best in Ryan's BRS/WWC Flow episode here!