Ok no I am wrong, it did unlock with Iconoclast on my second ending...somehow I didn't notice the popup (maybe a bug of the new steam interface). So my post below actually works.

I only had a black eye in the end of the game and didn't get Stoic. I did torture the guy in the chamber. I never got caught (whenever I got caught I reloaded a save, should work). If I got caught, I didn't wait for the respawn but i would quit to the menu without saving.

I actually got the Archivist achievement when I picked up a memory canister.

Hello, thank you for that helpful guide! I was just wanted to point out that one of your ending achievements has a wrong picture in it: Iconoclast

I just wanna add that the game got an adventure mode which basically removes enemies pretty much (at some points there are still enemies but they won't chase after you and they can't kill you, they will only push you away when you touch them), lighten some areas more, you can carry more matches, and puts in more puzzles.
You can get all achievements in this mode except "Overlooked" and "Stoic".
Especially you can do "Speedster" achievement in adventure mode which I assume is a bit easier than in original mode. You will take more time for the additional puzzles but also win some time in the areas which would have enemies. I think the trade-off is worth it. I got the achiev in 128 minutes, including loading times, without any glitches and I still made some small mistakes.

I must say the speedster achievement wasn't as hard as I expected, even without major sequence skips.

Here's how I got the speedster achievement:
I read in another guide that saving and reloading doesn't affect the in-game timer (time spent in game menu, item menu and loading time neither), so you can re-run a segment or level until you're satisfied. I've only used a few small skips that I had found myself.

Generic tips:
- you can withstand darkness for a surprisingly long time
- you can take a LOT of fall damage
- there are so many places where you can ignore ghûls and just run past them; their reaction time is slow; hiding only costs you precious time
- there are 3 places where a scripted sequence only starts after you get caught by an enemy; not trying to avoid this will obviously speed this up
- don't look around for matches and oil, there are enough opportunities to pick them up on your way
- take the laudanum if you're about to loose control

The check for Stoic actually just checks if Ghoul Progression is higher than GHOUL_PROGRESSION_<ENDING>_HIGH , which is 9. This just means you can't permafail more than 9 times. This includes scripted permafails, so just try not to die more than a few times.

There are only 2 states. There is a hidden counter from 0 to 20 in the game, and if you end the game with >= 20 then you don't get Stoic.

A note on the Stoic achievement, definitely tied to how far you ghulification progress in the game.

I got caught (QTE-struggle, not ended) x3 times in total throughout the game, all 3 of was by the Wraith. So as long as you don't "die"-lose control, you can tank some hits.

-Ended with Provider ending.

While I don't think it matters for this in anyway, I didn't do the torture and went the Altruist route.

A good pointer if you'll get it, is the fountain reflection right before the elevator as you can see from much you've changed and Tasi will comment on this.

I got Stoic with very little change, a black eye for most part and the comment:

Well. I thought it might be worse.

While there is probably more then 2 states of the ghulification, you're golden if you get the first line and pass as human. In another playthrough, where Tasi was clearly too far gone the comment was You're a monster, Tasi Trianon

Hope it helps!

@Darkcastalone It took me a bit to do, but you've got to hold it close to your body and look down at it and push it against your upper body