My holy grail size for 5K 16:9 is in the 29-30" range, although I'd take a 32" too.
27" 5K = 218 ppi, Retina at 15.80"
29" 5K = 203 ppi, Retina at 16.97"
30" 5K = 196 ppi, Retina at 17.56"
32" 5K = 184 ppi, Retina at 18.73"
Ergonomic guidelines recommend a minimum 20" seating distance for a desktop monitor, so all of these meet that criteria for Retina.
If we are on the topic of holy grail give me 4:3 aspect ratio or at the very least 16:10 like Macbook Pros. I remember one day walking into a Microsoft store and playing around with the Surface Studio(28" 192PPI 4:3) and it blew the 27" 5K iMac away yet was only a 1" larger. The iMac felt so cramped using it compared to that glorious IMAX aspect ratio in a monitor. Holy grail for me would be the 32" Apple XDR at 4:3.
