Floor 200. That’s where all my farming adventures began and where I usually get the most gold, EXP and crystals from so many Eternals.
Floor 500 is definitely a great choice to farm though because you can get absurdly amounts of emeralds, peridots, etc and a lot of rare crystals given the high item drops and no need for luck affix to do that. An awesome place to especially get High Rarity mythstones and crystals. Definitely great to do, especially on easy mode where you one shot them all (although you could still one shot them without easy mode).
I use a farming hero and farming hirling combo. Although I used to use a farming fortune bringer with a pure DPS hirling but it gives less of the farm affixes despite the damage bonus. Besides, Arcanist already made farming super easy at floors 500+ . Same combo cronos used but I decided to scrap it due to high inefficiency. It is fast I can give you that.
But currently I’m working on a new farming build to be even more efficient than before and to farm 3 individual classes as hirling combos to make legends drop the most efficient for that specific class.
you’ll definitely notice the difference between 200%+ item drop from 100%. Once you have better gears and you have 300% item drop with 800% luck you’ll get legends, crystal legends and eternals on literally every single map
Yes mythstones can be removed from Eternals. Just use a garnet and BAM! But only do this if the Mythstone you remove is valuable: I.e. Elixir, Master, Zenith, and anything that rare.