After doing some additional experiments here some summary.
My findings here focus Delta E* using the CIEDE 2000 formula. A possible interpretation DeltaE* may be:
- DeltaE* = 1, barely detectible
- DeltaE* = 3, visible in images
- DeltaE* = 5, objectionable deviation
I found that of my two cameras tested the Sony Alpha 99 had the lowest DeltaE* using Adobe Lightroom 5.3 with a home made DCP profile, but Adobe Standard profile was close, so I will normally use the AdobeStandard profile on that camera.
With the P45+ the issue is a bit more complex. What I found initially was that Lightroom 5.3 with both Adobe Standard profile and my home cooked DCP profile produced smaller deviations than the Studio flash profile in C1 I compared with. But, I also know that I was not satisfied with the Adobe Standard profile, the very reason I generated my "dcp" profile. Very obviously Delta E* doesn't tell whole story.
Switching to linear curve improved the statistics, with linear curve C1 produced small deviations, almost as good as the Sony.
I would presume that DeltaE* takes both Luminance, chroma and hue into account, and the film curve varies luminance intentionally. Using the linear curve I assume L stays linear/straight in some sense.
So this would indicate that linear curve in Capture One gives good rendition and my guess is that film curve just adjusts tonality.
I also made a comparison between "Portrait natural" and "Flash" in C1 and the differences were very small (way below DeltaE* = 2 on individual patches) and mostly in areas nearly skin tones. I presume that we see some of the "image professor's" hand at work. Very small subtle effects in selected areas. Delta E* mean between the two was just 0.51. I enclose the comparison between the linear profile and portrait profile.
The outdoor daylight profile and the flash profile were essentially identical, no deviation at all.
Personally, I feel I have learned a lot about the options I have at hand.