I finally made my choice: it will be Capture one, with Photo Mechanic support for ingesting, sorting out and keywording. My new workflow:
1- Import from camera (D800) to a temporary folder with PM: easy and fast keywording and other metadata (weakness of C1), eliminate what belongs to trash. Possibility also for external editing (e.g. Nik filters) if wanted, why not. I loaded into PM my Aperture structured KW list(s).
2- Move images from temporary folder to external drive with my folder and file naming convention: PM is extremely powerful for this job and for creating a backup copy, incredible.
3- Import the pictures into C1 catalogue. No need to bother with the weak KW / metadata options of C. The C1 search is for me powerful enough to retrieve and sort pictures (smart albums) on the basis of metadata from imported Aperture libraries and from PM tagged images.
From Aperture (referenced) to C1: it simply requires some time:
1- Copy in Aperture metadata to originals. Works perfectly per batch of 2000 - 3000 images on my system. Freezes for the whole library (25k images).
2- Import Aperture library into C1 catalogue. Just leave time for the catalogue to create the preview images for which I took a reasonable size (1080). The C1 catalogue is…. much smaller than the Aperture library, that was unexpected from what I saw in the litterature. Time to open the catalogue is 5-10 secs, for 25000 images, initial view: all photos. But all preview images have already been created. I can live with that, vey well.
Settings: folder sync, pref. side car file to original for metadata. If auto sync side car is on: the catalogue freezes, I indicated that to C1 developers.
I found again the full structure of the Aperture library (albums / projects), can easily rebuild the KW based smart albums. For the edits, I almost exclusively externally edited from within Aperture and had therefore TIFFS together with original files. If not, a JPEG version from the Aperture edited files can be created.
I am not sure that I would like to get rid of PM at the import stage, I have the feeling that it gives me more compatibility than relying on only one software.
Bye for now, Aperture!