Road & Track (I think, but maybe it was Car and Driver) did a study on this once. They found, through theory and experiment, that the most fuel-efficient driving (assuming starting from rest to achieve any given constant cruising speed) involves two techniques: The first, as one would expect, is to use short-shifting (shift at low rpms but without bogging). Second, and far less intuitive to most, is to use nearly wide-open throttle while accelerating.

Even when short-shifting, it takes a certain conviction, I've found, to start flooring it repeatedly when the gas light goes on. It's also a good conversation-starter if your passenger notices.

 

Another twist on this is to use the cruise control whenever possible.

This has two advantages:
1. You keep a constant throttle/fuel feed while in cruise control mode.

2. If you are accelerating punching the cruise control button gives a smooth but wide open throttle very fast, feels like mini nitrous.

However you must be in a forgiving gear like 4th.

 

[QUOTE]Originally posted by Silver Bullet
[B]In my normal-driving mode, I usually shift into the next higher gear every 10 mph.

For instance, 1st to 2nd at 20 mph, 2nd to 3rd at 30 mph, 3rd to 4th at 40 mph, 4th to 5th at 50 mph, 5th to 6th at 60 mph.

 

ECM goes into "Open Loop" at greater than 25% throttle and greater than 5000rpm, so there are your upper bounds to the question at least. The true "best" probably lies somewhere beneath