I just started farming chaos plains+bone pits a couple days ago w/ a slightly modified perma sf build I got off of pvx wiki. I had never farmed uw before, and never done perma sf before (though I did practice the timing before I went in) and screwed up a lotr in the beginning. Even now that I can use the build perfectly, there are still some times when the obsidian behemoths block the passage so you can't get by

However, this run is insanely profitable; my first complete run (aka I didn't fail halfway through) I got 7 ectos, 2nd 4 ectos+ruby, 3rd 7 ectos+ruby, 4th 8 ectos, and my most recent one 10 ectos+sapphire. This might just be because of the large number of foes though; there are 208 ecto dropping foes in the chaos plains, and I don't know how many in bone pits, I'd estimate somewhere between 25 and 50 though.