8-3/4 Pinion Nut Torque???

You can far exceed that torque with an impact. But as a general rule, I avoid using impacts with mechanical element bearings, except for disassembling something that is going to have the bearings changed. But the torque is usually high enough to be a concern with how the car is supported and what you foul the pinion flange against when tightening it. It's easier than most realize it is to lever a car off of jack stands.