The MOP penetrates by concentrating a lot of force onto a small area, it does this by being highly dense and very long.

Velocity has diminishing returns for penetrator performance beyond a critical point, depending on the material properties of both the penetrator and the target.
The penetrator will begin to deform beyond the critical point, then it will turn completely fluid, behaving more like a jet of water.
Rock (IE silicates) targets actually have more unfavourable characteristics compared to metals for extreme velocity penetrations, as they do not deform plastically in the same way.