The Coulomb collision transfer rates for energy and momentum exchange between drifting Maxwellians are evaluated. We discuss the associated time scales which depend on the masses, densities, temperatures, and velocities of the two colliding species. Inclusion of finite mass density effects of the minor species generally leads to shorter time scales, as compared to the test particle approach, for any differential speed and temperature equalization. We find that two particle species may, by collisions, attain a temperature ratio which can range between 1 (thermodynamic equilibrium) an the inverse ratio of their mass densities. This result suggests the possibility of preferentially heating the species with the lower mass density by Coulomb collisions, assuming that their differential speed can be externally maintained against frictional deceleration.