interesting topic
i think the rear diff is the weak point, the same as the gear boxes are.
gears are always a weak point
the point where the tuch each other there is created a hough amount of heat
also the point where the gear is connected to a shaft is weak, because it is not a one piece
the metals density is effecting the heat up process, you need a high density steal to reduce heat.
i know heat treatment is a way to dense steal, but freezing sounds more the less the same, only as far as i know it makes it more brittle.
make it strong enough to hold hugh power is a compromise between flexibility and strength.
i think upgrading the rear diff and checking the prop and drive shafts on purety will give you a greater change to survive the amount of force you will create.
forching a engine is the normalst thing around here, only upgrading gearboxes stops at putting a LSD in.
everybody knows a 6speed has it limits
there are not that much companies who rebuild and upgrade gearboxes or differentionals.
i was looking into rebuiling companies who upgrate gearboxes but they arn't easy to find, also as rebuld is far from cheap.