This actually sounds thought-through and rather curious. I have to agree that a "gearbox" system would be more beneficial than the fast/slow/regular driving modes, especially on systems without analogue controls; Analogue controls, as well, could get the benefits of the system as well (incremental throttle).

As an extra thought, slight modifications of the existing vehicles' dashboards would be needed to reflect the relevant information (I believe helicopters do so as well).