Howdy all,
Let me first say that gearing changes are not a durability upgrade unless you switch to a single chain setup.
There are many other components that have to be addressed in order to build a piece that can take the whoopin that you monkeys put on a trans. Torque converter
and turbine shaft are most important.
Driving habits, and tuning scenarios are factors when
trying to determine the life of a transaxle. With all of this said, it is really a crapshoot to try to assign a lifespan to a transaxle.
BIG JEFF