The item level of its contents are determined when it is acquired, but the item stats are not determined until the cache is opened. For example, if a level 70 Demon Hunter acquires a cache, and a level 60 Witch Doctor opens it, the loot will roll at level 70, but Smart Loot will roll stats of the Witch Doctor. Torment-only legendary items (including the legendary potions) can only drop from the cache if that cache was obtained on Torment I or above. "Within their monasteries, the Horadrim amassed treasures great and small. As the order was forgotten, so were its secrets."