This might be of interest.
Toyota geared the overseas FZJ105s with 4.30 gears. The FZJ105 being the 100 series with basically a 80 series frame and suspension and the 1FZ engine, but also included a 5 speed manual tranny, which had even lower gears than our 4 speed auto, including overdrive. So, for whatever reason, Toyota felt it was necessary to have the 105 run at a higher rpm at highway speeds with this vehicle and the same engine as us.
My guess is the one factor nobody has really brought up in detail. Weight. The 105 weighes a lot more than the 80 series. And most of us that modify our rigs...even with just 33s, probably have a lot more weight than a stock 80, by virtue of winches, bumpers, extra gear.
Add a lot of weight and suddenly the engine is falling out of it's effeciency band to push the same vehicle at the same speed at the same rpms. Effeciency is not just a product of rpms. It's also product of how much fuel the engine has to burn at a given rpm, which is determined, among other things, by throttle position.
So, lowering rpms or raising rpms doesn't necessarily improve gas mileage all by itself.
If one adds a ton of weight to an 80, like the roughly 1700lbs I've added and then adds taller tires to boot, regearing is going to be necessary to return the engine to at least some of its former operating effeciency. Although it will never return 100%, since the engine will always require more fuel to perform the same amount of work at a given speed, no matter what, due to the added weight.
But when regearing, one should probably take more into account than just the tire size difference. The difference between 33s and 31s (in my case) is about 6.5%. But I've added 24% more weight. Obviously, the weight difference is not linier like it is with the tires, but that's a pretty significant factor.
By my calculations, 4.30 gears would compensate for the tire size increase. While 4.56 gears should copmensate properly for the added weight, meaning for at least my purposes, 4.56 or 4.88 gears would probably be the better choice.
I don't know how regearing affects perceived drivability in the 80, because the 80 has a lot of excess power, even though many of us don't really see that. But in the far less powerful Toyota mini-trucks that I come from, regearing, even moderately, from 4.10s to 4.56s makes a WORLD of difference when compensating for taller tires. While I ran a variety of different tire sizes and gear ratios, at one point I was running 5.29s and 33s and it made a huge improvement, but the 22RE engine I was running operated very effeciently at a much higher rpm than our 1FZ is probably used too.
Same planetary geared 1st, torque rating. "school bus tranny" 
