The major difference is display and PPI on that display. It is around 530PPI vs 800PPI on Pimax8K display.
This PPI is a major factor for SDE but it is not that bad. For example, Vive PRO and Samsung Oddisay have displays with almost same PPI.
PPI is Pixel Per Inch and is represent a physical resolution of the display. A smaller number of PPI means larger SDE. For better understanding and comparison check this video.
Vive and CV1 have 450PPI Deepoon have 530PPI same as Vive PRO, Oddisay or Pimax5K, and Pimax4K as Pimax8K and 8KX.
Thet is only about SDE. Minor effect on SDE has Optics that is the difference Vive and CV1.
The second difference is PPD or Pixel Per Degree. This represents resolution display is capable to run better known as native resolution. Vive and CV1 have horizontal 1080 pixels and around 100° FOV per eye. Dividing Horizontal resolution with FOV per eye you will get PPD value. Here some examples:
Vive, Pimax4K and CV1 - 1080 / 100 = 10.8 - around PPD in 10
Vive Pro, Oddisay, other WMR - 1440 / 100 = 14.4 - around PPD in 14
Pimax5K and Pimax8K - 2160 / 150 = 14.4 - around PPD in 14
Pimax8KX - 3880/ 150 = 25.8- around PPD in 25
As you see the difference between 5K and 8K is in SDE because 8K PPD will be the same but on more quality display. 5K should have similar quality as Vive PRO and Odissey in any technical aspect should be the same as a 5K model only 5K will have double higher FOV.
Pimax8K will have all that plus significantly lower SDE as well. Similar like Pimax4K compared to Vive.
Pimax8KX will be ultimate VR but for full potential will be possible only with some future kick ass GPU or after implementation of Eye tracking and Foveated rendering technology or technology which allow using single GPU per eye so we could run pair of1080ti. at least in high demanding games like Project Cars 2 or DCS for example.