I think the primary advantage of having more cubes for a given turbocharger size and therefore power output, is the transient response of the turbocharger when applying part throttle and also in gear selection when the rev drop between changes may fall in a better range of the power band.
basically, more cubes and therefore greater flow of the fluid (air) through the turbocharger allow the inertial threshold of the wheel to be overcome more rapidly in the situations described above, giving the power delivery a greater driveability but not necessarily tractability which comes down to how your putting your power to the ground.
Cheers,
Mitch.