What can a 7 1/4 rear take???

I have a 7 1/4 in a 70 Dart with a warmed over 318 and O/D 4 speed. So far it is taking the abuse but I don't dump the clutch. I do spin the tires but by gradually adding more power, not by shocking them free. Had a 67 Dart GT with a 328/904 and 7 1/4. Never babied it and it lasted for years. A sure grip would definitely increase the abuse it will take.