Well, the iMac has been delivered and I have been busy carefully building up my system. I do not like to use Migration assistant, rather I freshly install whatever I really need. First: the screen is really gorgeous!! Sharp, crisp, which is clear in e.g. the Lightroom lettering. Good for my eyes. Also the color space is notably larger. I took a picture of a red tulip field I made last spring and you can see the difference on the 27″ Thunderbolt Display (now ‘old’) left and the new retina iMac right.
right the new 5K iMac
I have now all my old and new libraries on the 3 TB Fusion drive ready for use. Over time I may transfer old libraries to external storage. I just finished generating high res Previews, which really speeds up Lightroom (Other tips for speeding up LR can be found at many places).