I have only one vintage Superposed, my late dad's 20ga-26" circa 1957 in M&IC with solid matted rib. I coveted it when he was alive and hunting with it, and cherish it now.

That being said, I would take the sxs Gamba if given your choices. I remember when Manlicher marketed them; we sold them at the store. They are excellent shotguns and not commonly encountered. You can always find a deal on a Superposed, if you have patience, and you don't NEED two almost the same. But, when does NEED dictate our addiction?