I have the Pimax 5K BE (OLED) now at home and had enough time to check it out. The difference to the 5K+ and the 8K is only the display. So the resolution of the 5K BE is 2560 x 1440 per eye at around 82Hz. Display is OLED with pentile matrix.
I alread tried the OLED at the CES in Vegas, but its always better to have it at home to check some more games. So all in all I would say:
The 5K BE is really good for people that play horror games like Paranormal Activity The Lost Soul or space games like Elite Dangerous. The black levels are perfect, because if the pixel is switched off its totally black (not like with the backlight of LCD). Its really much more immersive to play these dark games. Also the colors are much better and not so “washed out” like with the 5K+ and the 8K. You see a difference here definitely.
However when we compare the SDE of the 5K BE to the 8K or 5K+ this is something you should really think about. The SDE of the 5K BE is really worse than the 5K+ or 8K. Perhaps even worse than Vive Pro. So if you really HATE SDE, then you should better not go for the 5K BE. For all other guys that want to have good black levels and good colors and SDE is not top priority, you should definitely consider to go for the 5K BE!
I for myself will switch the headsets… Playing horror games= 5K BE, playing everything else = 8K or 5K+.
If you want to check out my English video, I made some comparisons with optical zoom: