What breaks stuff is force, the unit of force in twisting is torque. Horsepower indicates how far up the engines rpm range that torque is made - gives you a good indications of a cars top speed, but not a accurate indication of how much drivetrain breaking force is available.

"The resulting torque fed to the differential is a multiple of the rpm at the motor." - I disagree, the torque value is not multiplied by RPM - it can be constant across the entire RPM range of a vehicle in some cars. Torque is independant of RPM

Have a think about how big diffs are in trucks, these things have very low horsepower motors with phenomenal torque figures...

Smaller scale any diesel engine really, poor HP, good torque.

In F=ma the F is torque the m is mass - so to determine how fast a car accelerates you use torque, then derive the abstract concept of horsepower.

...I think i've forgotten what my original point is... but in summary force breaks stuff and torque is a force.