I have been running The Core of Arreat the past 3-4 days on low torment or even all the way down on normal. Since the drop chance for legendarys doesn't scale up by entering tormented this is possible to farm with pretty much max potential with just 50-60k dps (I do this with my wd or barb, both really well geared, but not a req)
What you aim to farm is elites, chests and vessels, I made a map of where chests/vessels spawn in this zone.
Each dot mark a chest/vessel spawn, avg you'll get 5-6 spawns per run all with a fairly high chance for legendary drops, ontop of that this zone always has 2-3 elite packs, I believe 4 is even possible and last but not least, this zone seem to spawn a goblin about
50% OF THE TIME!