Rear end question.

[shrtbx]

Seems like i read a thread once that said better mileage if you get gears that match up better with your engine. I have an 86 swb with an edlebrock 1904 on top of a 350 with a 700 r4 trans. The truck has 3:08s in the back. I read a few posts that said you can waste gas with the 3:08s because it takes to long to get up to speed and maintain a certain speed without having to give it gas. I hope this isnt too confusing but could i get some input on this.