A lot will depend on how the car is used also. I can tell you this that I bracket raced a 340 Dart back in the late 70's and early 80's. It was a 4-speed car and ran low 12's with a best ever et of 11.94 @ 113. Now when I launch a 4-speed car the gas pedal goes to the floor when the clutch comes out. In 4 years of racing the Dart I broke at least three 8-3/4 rears. Tore all the teeth of the ring gear once. Broke the pinion teeth once and broke the carrier once. Now fast forward to today and I have my 63 Sport Fury with the 8-3/4 rear in a heavier car. But my 63 is a 727 auto car. Its run 10.70's and it has never broke the 8-3/4 in it. I only race it about twice a year but its been on the road and raced some since 2011. The stick shift driveline is much harder on the rear if you run the car hard since it shocks the drivetrain. With an auto street car and street tires that don't hook the 8-3/4 should hold up fine. But with stickies it will depend and with a stick car it will be even worse. Ron