One of the mistakes people seem to make a lot with gear selection is that they don't realize that they're giving up something in return for more torque.
Gears are kind of like a lever. If you increase the length of the lever on the side of the fulcrum you apply power, you'll be able to move more weight with less effort but you won't move it as far.
With gears you are able to apply more power to the wheels, but your power band runs out quicker, limiting the speed at which you cross the finish line.
My guess would be that the optimal gear ratio would have you going through all the non-overdrive gears and having you cross the finish line just as you pass your peak horsepower. Too much gear will have you out of your powerband too fast and you'd be loping through the finish line and too little gear will have you starting slow and accelerating through the finish line, wasting power.
Oh, the performance difference between 3.73s and 4.10s would be less than the difference between 2.73s and 3.08s.
Whenever someone asks this question, and if someone is going to answer it correctly, the thing they need to know is where their powerband starts and ends.
I may not be exactly right about what's optimal, but I thought I'd throw that out there as a baseline for discussion and to get people thinking about what is optimal for a specific car rather than some guy with a stock engine asking someone with a race engine what they think of their 4.10s vs 3.73s.
I hope no one takes this message the wrong way. I'd just like to see a more thoughtful discussion on how to pick gears and not just apples telling oranges why they picked their gears.
BTW, I picked 3.55s since I already have tons of torque but want to keep my top end somewhat.
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351W 89 Mustang GT Convertible