Prior to my buying a Sinar 54 H, I would have agreed with your experience, that scanning backs are the best means for fine art reproduction. What I found that helped me to change my option and subsequent buying decision, was that all the museums that do reproductions use the same Sinar Bron equipment and not scanning backs. When asked what helped the Museum of Fine Arts Boston, The National Gallery Washington, DC and several others, what led them to decide on Sinar multi-shot backs and Broncolor lighting, they provided lots of compelling reason, not least of which is the fact that in the 16-shot mode the file size of the 54 H is twice that of the Better Light back. No need for hot continuous lights, and consistency of color.
I realize that you are happy with scanning backs, but thought that I would respond to your question, "...what is better for reproducing at actual size large paintings?".
HTH