Text sizing on both the 27" iMacs, Retina and non-Retina, is exactly the same, but it's small enough that it becomes harder to make out at my preferred seating distance. On the non-Retina 27", it's just annoying overall. It's noticeably better on the Retina 27", but the default text size is small enough that it's still an annoyance. To make it feel larger, I need to sit closer, but this is a problem since it becomes harder to focus with my progressive lenses if I sit so close, and I find it tiring over time. A solution to this is to get dedicated computer glasses, but they are not suited for other uses, so I'd have to be swapping glasses all the time, which is even more annoying, and which also makes me nauseated.
OTOH, for the 30" non-Retina display, the default text size is large enough that I can sit at a reasonable distance that makes it less tiring to focus upon.
Thus my holy grail screen would be a Retina screen but with a LOWER pixel density than the 27" 5K iMac or 27" 5K Studio Display. My holy grail screen would be a 5K 5120x2880 29-30" screen, which would provide a pixel density of 196-203 ppi.
However, in the meantime, I will continue to use my 101 ppi 30" Cinema Display. And in fact, when the Mac mini gets updated with M1 Pro or M2, I will buy one to use with that same 30" non-Retina display.
What about a 4K 27" screen? Nah. I don't really like those. The font sizes are even larger but the screen real estate is not wide enough. I want at least 2.5/5K wide, not 2K/4K wide.
I just picked up a Dell UP3017, which is the same size and pixel density for this exact reason. Sure if I moved the screen closer I could deal with 27" 1440p, but I lose desk real estate that way and I like to recline at times.
I had a 24" 1920x1200 monitor before this which was an even lower PPI of 94ppi which I also enjoyed.
I'm also waiting for a 5K 29-30", heck I could go as big as 31.5" if I had too, but the 30" size would be just about perfect as it would be in between my two monitors. (And while the added height of 1600 vs 1440 is nice I don't think I'll miss it much and would gladly trade it for HiDPI)