Rear end gearing tech question

Dana said

Think about optimizing your setup based on torque curve. If you are going to dyno the motor, see where the torque really starts to climb and plug in your tire size and different gear ratios until you find the one that puts you at cruise(70mph) just into your particular torque curve. Example: If your combo don't start making power until 2500, don't be cruising at 1800. If you are not going to dyno, then at least you can use the cam manufactures rpm spread. Wallace racing .com has easy to use calculaters to help figure.

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I've seen people recommend this before I don't get the reason why. Could you explain?

Especially since the dyno measure WOT power (torque) and on the highway you'd be part throttle.

My 380 hp create engine which probably peak torques around 4000 rpm. Will cruise fine at any speed as long I'm over 2000 rpm far from peak.

As for the OP you left out the main spec your cam size that will tell us where your powerband is.

My car unfortunately has 2.96 gears right now but are liveable and if in the right gear at the right speed can be fun but a set of 3.91 will make it fun in any gear or speed.

As for your car especially supercharged you pretty much could run any gear from 3.23-4.30. So 3.73 is a good choice most will probably say 3.55 for highway driving but it's up to you where to draw the line.