Well, this popped up a while ago on Reddit, and I've waited for a long time but no one cared to re-do the chart. And since there are now approximately 23 threads per minute asking those questions, I thought I'd just give it a go. So here's the somewhat updated difficulty overview:
Disclaimer: Many of the values are guesstimates - solid guesstimates based on lots of work, but not exact science. In GR key drop rate and some T11-T13 data, like DP drop rate, could always benefit from more data.
I'm kind of surprised that there's no info about the GR key droprates below T6. Does no one have this? Or is it just so relevant as most people are on T6 after a few hours or days of playtime every season and anything but T6 rifts becomes irrelevant?
If anyone has any data about that - as vague as it may be - let me know.
@Aterin: Yeah. Someone on Reddit said that expert seems to be 150% in-game though... need to check. I mean, this is taken from the game guide...
Note that the Keywarden drop rate is still completely up in the air - several people on Reddit report it's much lower. I made a new chart (http://i.imgur.com/06y2nBY.png) but still looking for more data... whenever you do Keywarden in the coming days please be so nice and collect the data, the higher the sample the better!
Keywarden drop rate is rubbish imo, got nothing three times in a row, I don't believe in coincidence. Droprates are still higher than they used to be though, so I'm not complaining.
Edit: did some more hours of farming and I came to the conclusion that droprates have NOT improved from pre 2.0.3. Most runs it's just 1 or 2 out of 4, 3 if I'm lucky. And I've never found 2 machines at once. Is this intended?
Friend and I did some Keywardens and found that not only can you no longer split farm them (they do not drop if you are in a different act, possibly even zone but we didn't test that far), but the drop is no longer shared as well (as in you can find one and your friends may not). I know it's not exactly drop rate related but useful to know. Or maybe it's already common knowledge? I didn't play S3 so I could be behind. I know that in S2, you could both split farm and the drop was shared. :\
Also, I personally never saw a 2x machine drop, farming wardens on T8 (which aligns with your chart, just saying). Farmed about 6-8 of each one. Did not confirm with my friend if he ever saw 2.
We did Ubers on T10, and got 2-3 organs every time, again as expected.
Okay, thanks everyone! I massaged the data, some of that by quite a bit, as especially the Keywarden machine drops seemed to be completely pulled out of thin air. As I'll run more Keywardens this week I'll try to keep an eye on that but for now I think the data previously reported was bogus.
Just tossing in my few coins - I farmed Infernals today on hardcore T7 and as said above, you must be in the same zone when the Warden kill happens to be eligible for loot at all, and even then it's random from person to person. So no more group loot for machines and every player has their own chances at obtaining them. Kills split farming
Also we ran 4x Ubers on t7 and each of us (4 players) received double reagents each kill, so all of us ended with 8x organs per boss from 4 runs.