[Blue Bomber Man]

Because only about 20% of a vehicles energy actually makes it to the wheels at highway speeds a lower RRC is still more valuable than improved gearing.

A 10% increase (in efficiency) at the engine only results in a 2% mpg gain.

However, like I said, the best tire I've seen so far is in fact a 14" wheel, so you would do well to work with that if you car's rims can take it, and then modifiy your transmission or final gear to gain any engine efficiencies through rpms