The prints have been delivered and an initial inspection has highlighted several points:
- The photos need to be brightened even more, although not by much.
- With the photos using the "Perceptual" rendering intent the reds seem to be more orange than red.
- Not sure whether it is my eyesight or the ambient light but the border of the photos were the ICC Profile is applied appear to have a very slight colour cast.
Overall I am at present leaning towards using the ICC Profile with the "Relative Colorimetric" rendering intent plus Photoshop adjustments, although further examination is required especially under different lighting conditions. I will probably make some further adjustments, especially on the brightness, and re-submit them for printing.