Help needed with choosing the optimal Dirac curve

[hellblau]

Generally speaking, the target curve should be close to a straight line (like in your first image), usually with about a 1dB/octave slope from bottom to top range.
Trying to copy the bass ambient response with the detail shown in all the other images you posted is totally pointless: human hearing sensitivity is low in this area, while it is much higher in upper midrange (2000-5000 Hz), therefore fine adjustment of the frequency response in this area does make sense. (fine adjustment = + - 2-3 dB, always using "gentle" slopes).

Here are my Martin Logan Electromotion ESLs in my room: the red line is the reference target curve.

 

[hellblau]

I've been using Digital Room Correction for more than ten years now (in the beginning with the TacT digital preamplifiers), so I could try different loudspeakers, different rooms and, yes, different target curves.
I said "generally speaking" and "usually" because your experience, the music you listen to, your sensibility end personal taste may vary, thus leading to different target curves and different ambient responses (including an "almost flat" frequency response).
What I can confirm is that targets with "mountains and valleys" cloning the ambient response are, in the best case, useless, especially in the bass range (20-300 Hz). The rest of the range can be "tailored", with slopes, valleys (the old fashioned "BBC dip" at 2000 Hz being perhaps the most famous example) or gentle peaks copying the ones of the natural response of the system (loudspeakers+room).  The less the target is above the measured response, the better.

[hellblau]

1 hour ago, STC said:

I am unable to comment on TacT room correction as I have never used them. However, I did use REWeq extensively before completely abandoning them for no correction except by physical means [cut]

 

If the combination of loudspeakers and room allows, by only physical room treatment, a satisfactory frequency response, that's a lucky strike.
Usually the owners of the typical European apartments' (small) rooms are not that lucky, so the DRC is a life-saver especially in the bass range, which cannot be tamed with surface room treatment.  :-)

 

The BBC dip was introduced - as far as I know - to counterbalance the excess of upper high frequencies (2000-5000 Hz) due to close miking of - tipically - acoustic instruments (violin, piano, etc.), in comparison to the "natural" sound of the same instrument in an auditorium. The spectral distribution of close miking often made the recording sound "too brilliant" compared to the real world listening esperience.  Anyway, we're talking about the recording technique of the '60s.