Awesome! Thanks for your input. Mike Wuerthele said:
LG's 4K USB-C and 5K Thunderbolt 3 displays will have the same pixel density as your iMac screen will. The panel in the LG 5K is the same as in your iMac!If you're looking to spend less, a 28-inch 4K display from nearly anybody for about $350 is close at right around 170 DPI. Use a USB-c to DisplayPort or HDMI cable to connect to the iMac.