OK so the power to the wheel to move a certain weight vehicle a certain distance is the same AT THE WHEEL, how it gets there can be different, so the amount of torque that must be applied to the half shaft is the same unless you change the ratio of the geared hubs.
Now the ability to deliver a given amount of torque to the half shafts changes with the ratio between the engine and the half shafts, it is easy to understand how you can deliver more torque to the half shaft with the transmission in first gear rather that in say 3rd gear because the torque is being multiplied by the higher drive ratio between the engine and the half shafts, (the amount of turns the engine has to turn to then turn the the half shaft 1 turn is higher)
So all the ratios between the engine and the half shafts effects the amount of AVAILABLE torque to the half shaft, so multiplying the engine/transmission/transfer case by 3.08 rather than 2.56 makes more torque available at the half shafts, but of course it has to all equal out so it takes more torque at the driveshaft to deliver X amount of power to the wheel with a 2.56 differential than if you had a 3.08 differential.
For those of you in Rio Linda torque is the amount of rotating force or "twist" and is usually measured in pounds feet in the USA
Edit, so the amount of torque needed at the half shaft to climb over that rock is the same no matter what is between the engine and the half shaft, so in that respect it matters not what the ratio of the differential is, only one has the ABILITY to deliver more torque with a 308 gear rather than a 2.56 gear so it will be somewhat easier to bust a half shaft, the same concept as it is easier to bust a half shaft in lower speed range rather than higher speed range (again when in "low range" there is a higher ratio between the transmission and the differentials allowing more torque available to everything between the transfer case and the wheel.