All this brings me to the question -what are your goals? To be able to claim the highest sustained power? Win time trials? Post Stravas? Or win races? Mass start racing brings another element into the picture. Races aren't (usually) won by the rider with the most sustained power but they are always won by the rider who manages to get his front wheel across the line first. Coaches often train their riders to use lower gears and higher RPM than optimal for sustained power because that rider will have taxed his muscles less over the first 95% of the race. Burned more fuel, yes. But he still has muscle fibers that can power that big gear for the next 5 miles to the finish. The guy at the lower RPM who has been cranking that power more efficiently all race won't have that reserve. Yes, he still has fuel but not the legs to use it. Coaches have told their riders many times - if you can out spin your competitor all race, you can beat him at the end. (Now, we all have different optimum RPMS as others above have posted so that "rule" doesn't always work. A Jan Ullich outspinning a Lance Armstrong would NOT be a formula for Jan's success.)
And for us regular riders - if we do this (slightly lower gear, higher RPM) we can have that reserve when the big hill comes or we arrive at the town line sign. We will still have the muscle for that steep grade or the massive gear for a minute or two. Drawback - that slightly too fast RPM often isn't much fun. Slightly harder on crotch. Seats want to be better dialed in. The miles don't fly by as fast. (Our mental timepiece is altered by our leg rotation. Spin more and it takes more mental time blocks to ride that mile.)