As theluggage says, the non-integer scaling isn't as good as the standard mode, but is still very good. Far better than on the OP's non-retina screen. I played around the the scaling modes a lot when I had a retina MacBook Pro to get as much working space as possible, but ended up back at the default because it was the right size for text readability, not because of scaling issues. I have never felt the need to play around with my iMac as I have a reasonable workspace on the 27" screen, but did test them as I explored my new machine. All were fine, just not quite as good as standard 2x.
One extra point about reading values in indesign and premiere, they will be lessened even at the same size because the text will be more cleanly defined.