rear ends.

Wut??

 

My opinion.

If you want a good all around gear for 80,000 lbs, look at 3:70's with 24.5 rubber, or 3:55's with 22.5's.
I drove many trucks with these ratios, (between 425 and 460 hp), and they worked well for a variety of applications and weights, up to 105,000 lbs "on highway", vans, reefers, decks and trains.
I've also been a bit off road but nothing really severe.

If you find yourself in a situation, like letting it roll down a big hill, or passing a vehicle that gets caught in your draft and speeds up without knowing it, these gear sets are good for 80 mph and a bit.

Your engine will be running nicely in it's power band at 60 to 65 mph and give you decent economy.
The problem with going to a faster gear is you loose low end grunt because your low gears also become faster, which causes your engine to work a lot harder at the low end.
It also put's more stress on the rest of the driveline, so if you wind up delivering in a farm yard with soft ground the steeper gear is going to make life a lot easier on you and the truck.

If you run the mountains and hills all the time or you pull over 90k all the time you might consider a gear step lower.
If you're always on hard flat ground you might consider a step higher.

Something I thought up one time was a set up with 3:08 rears with an 18 spd and Eaton 2 speed auxiliary transmission.
Can't remember what the reduction was, low gear in the aux would have dropped the ratio to around 4:88 or deeper and in the top end you had 2 gears that would put you in the power band at 65 mph, direct and first overdrive, with top gear left over for going home empty, or coasting down long hills, top end over 100 mph, 114 mph sounds familiar.
Would have still been hard on the truck.

As someone else mentioned, a faster gear and lower rpm doesn't always equate to better fuel economy, it's your right foot, your gauges, your patience and how you use that gearshift in relation to those other things that create that economy.

Here in Canada the max weight for a set of super B's is near 140,000 lbs and the most common ratios are 3:91, 4:10 and 4:30 depending on tire size, with 500 plus hp.