pontiacjack,
The tradeoffs moving from hypoid to spiral bevel (0 offset) are:
1. The obvious that you have identified--packaging to floorpan.
2. Torque capacity is somewhat reduced, so you have to increase the ring gear diameter as a countermeasure, decreasing ground clearance.
3...
pontiacjack,
There is reason to believe your softer gears would perform better in an extremely short run situation.
If the failure mode is impact/overload, and the gear is at its limit for deflection in a given housing, it is probably being tip-loaded on the heel of the gear. In this case, IF...