Salaries

How does salaries work, I have 2 players, both same age same position and very close to same stats, yet the one cost 20k and the other one 6k, Does that mean that the 20k player will perform better on the field then the other one (Extra strength and/or speed in his base stats) or does that mean they will perform the same on the field, the one will just cost you 14k more to keep in your squad?