People seem to think this will be easy to drop, but that is not really true. Even with gheeds chance of dropping, will be really low drop chance in fact, because it can only drop from elites, uniques and super-uniques. It cannot drop from anything else, including the minions of those groups, because it does not says unique packs.
A good density terrorized zone will have around 5 groups, 2 elites, 2 unique and 1 super unique, lets say.
Calculating 3 mins per run you have the following with 0% MF:
Gheeds chance to drop fromIlvl 87+ Elites/uniques/superuniques:
Elites = 1 in 49606 (the pit elites)
Medium number of elites in a good density map = 7 (one pack of 3 and another of 4)
Total chance = 0,0141%
Uniques = 1 in 22994 (the pit uniques)
Medium Number of Uniques = 2
Total chance = 0,0087%
Super Uniques = 1 in 49450 (throne of destruction Super Uniques)
Medium Number od Super Uniques = 1
Total chance = 0,0020%
Total run % chance = 0,0248% = 1 every 4000 runs
Assuming 3 mins per run you get 1 unique charm (including gheeds) every 200 hours of play from those sources (not counting gheeds from whites, act bosses and so on, because these cannot drop sundering charms)
Now, assuming gheeds will be 1 roll on 7 possible unique charms, you are looking to 1 sundering charm every 230 hours of play (wich can be any of the 6, including magic and phys charm).
You can also assume the game treat gheeds as 50% gheeds 50% sundering, wich would give you 300 hours of uninterrupted gameplay with great speed and density zones for one RANDOM sundering charm.
2 extra things to put here:
1 - 175 MF will divide the time in half, 400 MF in a third, in theory
2 - Magic and phys are so bad that you basically have to multiply the time for a good charm for 1,33.
If you make the resistances random with so much space as 75 - 125, that would be probably the worst and most rare item in the game for a good one, as you divide it be 50 types of each charm after you decide its a sundering charm and wich one you get.
P.S. With 0% MF its 20% worse than Cham at cow level and with 400% MF Worse than Ber, for a Random Charm including Gheeds.