Well, unfortunately I don't think there is a single answer to this question. Generally, the closer to 100% charge, the more degradation will occur, and the closer you get to 0% the same problem occurs. The pack is made of a bunch of modules (?96 if I remember correctly). "Pack damage" may occur if all cells degrade equally, but I don't think this is the usual situation. Usually one or more of the cells will degrade at a faster rate than others, and it is the weakest cell that determines the range of the car.
Turtle on my Leaf is about 3.000 v per cell, and below that almost certainly increases rate of degradation. That would be 3.000x96 cells=288 volts.
2 LEAFS, bought 1 week apart. 2013 S for me, 2013 SV is wife's. Both manufactured May 2013. I lost first bar at 36,000. Wife still has all bars at 50,000.