@Williammeke: The 4K Card will run smoothly depending on the base hardware independent of the type of monitor. In my case, both Mac 2012 (2VRAM - 8 RAM - SSD - 1080p) and Mac 2018 (4 VRAM - 16 RAM - SSD - 5K) run smoothly.
In 1080p the behavior is quite good.
You can update the Cards as follows:
- Check that you have the latest version of iStripper installed
- Touch a CRISTAL PLUS + Card and in resolution you tell it to go down to 4K, if the option does not appear, vote the CARD and reload it.
I leave you a test with video display at 1080p
Jenny Wild / 1080p Test Resolution
https://youtu.be/CB6VrStL9Ps