Thanks, I appreciate the practical example. I am not sure that the speed range improvement is a 1:1 correlation since the article states that the relationship Cz max/Cx min correlates to the speed range of the wing, which I believe is maximum load (so gross weight the wing must support) divided by minimum drag. That's just going to cover the induced drag from the wing, not any of the rest of the drag from the fuselage, gear, tail, etc. As I said before, I don't have the math skills at this point (35+ years since I've done much more than basic arithmetic and geometry) to do this quantitatively. My gut tells me that a reduction in induced drag all other things being equal will improve speed slightly and climb a little more.

One thing we haven't discussed is the behavior of the Nenadović biplane at high angles of attack. It appears to me that the Nenadovic biplane continues flying at angles of attack beyond the monoplane's stall, which could be useful in providing low-speed safety and perhaps eliminate the need for landing flaps, which would partially make up for the complication of building two wings not one.