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I would say the torque tube shaft is the weakest link and it will hold 1000 hp.  MACK

When you get to a certain level of HP, you are running road gear, which is direct drive. The standard 2-pinion differential needs to be "needled" on the pinion shaft gears and have bronze washers behind the side gears (from a WD45) when you get over 500 HP. I also believe in a bronze rub block behind the ring gear (like a semi-truck axle) to minimize spreading of the ring gear to pinion gear under load. With that being laid out there, it is all stock components 100% until you get to requiring gear speeds faster than road gear. 1200 HP at 6700 lbs with 24.5 x 32 tires happens all the time in my neighborhood without troubles (yet).

If you are actually going to put 100 HP thru it AND pull a 4-bottom moldboard plow, you'd better raise the oil level in the transmission (overfill) an inch or so. You also better have a dual wheel on the left side and fluid in the rear tires. The differential can be destroyed in short order on a moldboard plow with extra HP. When the left tire is out there scratching away for traction, the poor differential gears are going for a ride !!!