High permeability indicates that particle mass moves easily through a membrane.
High conductance indicates that electrical charge moves easily through a membrane.
For ions, which are charged particles, movement of mass and movement of electrical charge occur simulataneously. So higher permeability indicates higher conductance. However, the relationship is not linear. Doubling of permeability does not mean that conductance exactly doubles. But, after initiation of the action potential, the sodium conductance rises very rapidly, quickly becoming much larger than either the potassium or chloride conductance.