I guess in an attempt to freshen up the runs for this game, is it worth trying OldDark? It's been confirmed that gentle clipping exists in SS2 (a glitch prominently used in the Thief speedruns) and it shows great promise but I'm not so sure if it's worth going back to OldDark, depending on how many glitches are exclusive to NewDark. That being said, the only issue is that both the GOG and Steam version come with NewDark thanks to Nightdive.

After a bit of testing, it seems OldDark is just worse to run compared to NewDark. The relocation clipping is an important and a heavy time-saver compared to gentle clipping, which is a lot less consistent and leaves little room for error. My run ended with Ric at the pod door near the rumbler. Of all the doors, I wasn't able to gentle clip through it and without relocation glitches, the only way to get through the door (unless some other clip spots or glitches are found for OldDark) is by destroying all the black eggs. It seems that NewDark is far faster than OldDark

From a recent playthrough, some things I've found from testing are some major differences between OldDark and NewDark.

1. OldDark allows for gentle clipping. The issue with this find however is that there doesn't seem to be many practical applications for it (at least for now), as using it on doors will only get a person stuck. A lot of the doors that can be skipped via relocation clips can be gentle clipped but there's a high chance of getting stuck on the doors and wasting time.
2. A major one is that you can't relocate skip on rec. After the death glitch in medsci, the game on OldDark forces the player to stand back up after jumping (rather than being much lower which is required for the skip on rec).
3. Relocation clips do not work on OldDark. NewDark also has the option of disabling new_mantle in cam_ext, which allows gentle clipping but makes a some of the clips needed for relocation impossible

Do you happen to know if door leaning still works? Basically lay a relocation marker next to the door while standing, and then lean into the door while you use relocation in order to clip through the door (and push the button on the near side of the elevator, the one that goes from rec to command). You can get the access card to Crew Quarters after doing the shodan cutscene skip and then be able to door-lean through the elevator to get to Command easily

Is it possible to gentle clip through the door to the nacelles in Engineering? If you can, you can instantly make the old dark version faster. It's the door if you turn left as soon as you go into engineering right before the ladder with the hatch, there's a button on the other side of the door that opens the door permanently without needing to purge the radiation. Why is it there? No clue.

If you can get it, it would instantly make the run so much... weirder. It'd be interesting!

edit: i read your post. the answer is no.

Door leaning should still work on OldDark, though I haven't tried it.

Gentle clipping the door to the nacelles seems to be impossible, the door frame around it and possibly the door itself is too thick to clip through. Sad tho, I wanted to see how different the run could be too.

The biggest issue that I ran into in OldDark is the game forcing the player back in bounds after invincibility and all attempts to do relocation skips (half of which are impossible to do on OldDark since those mantles are only really possible with new mantle). Turning off new_mantle and doing this in NewDark does allow for relocation skips HOWEVER jumping at any point, either after the invincibility or after successful relocations (which can't be done normally, I did this through loading a previous save) causes the player to be forced back into bounds by automatically mantling the floor at the jump command. Also, since new_mantle is the reason why a person can mantle onto those necessary ledges for relocation skips, it seems that gentle clipping and OldDark is objectively slower.