Dempsey wins but not without difficulty. Schmeling gives him trials and tribulations on the way to victory.
Hard to say, Dempsey never beat anyone remotely as good as Schmeling, but he was more dominant and consistent than Max. Either Jack knocks him out early or Max takes him out late.
Jack was too fluid, serpentine and mercury for Max. Those qualities and his speed and power make me feel confident Dempsey would KO him.
My man Schmeling wins this one for a whisker. Of course, I am asumming Max brings to the ring the same kind of focus, accuracy and timing he brought versus Louis.