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sabot came from KE submunition, which existed at the time, or even before the russian started using PTRD. Higher muzzle velocity just meant more kinetic energy. The main concept behind the idea of sabot was a light filling that allowed gathering of energy more efficiently, and discarded during flight so all the energy would be transferred onto the smaller penetrator. Adding sabot doesn't make the penetrator go faster, nor does the penetrator accelerate after discarding the sabot.
Medium caliber today, 20mm, 25mm they can have as much as couple MJ of kinetic energy when fired at hypervelocities. and that's enough energy to move quite a bit of metal (roughly a car traveling at 200 miles/hour). How much metal get pushed away has very little to do with diameter of the penetrator (in penetration calculation the diameter is taken into count in the form of an added variable by L/D ratio), but does depend on how densely packed the armor material was. A 25mm APDS from bradley has more KE than a WWII german 50mm, it will make a bigger hole.
So vise versa, a WWII 20mm, probably had 1/4 the energy of a 37mm, which had about 1/4 of the KE of a 75mm. So a 20mm would probably make a impact crater about 1/16 the size of a normal 75mm (not a high velocity).