I bought my 4k twice, too:
I made my first steps in VR with Oculus Rift DK2 in summer 2014. The experience was overwhelming on one side, on the other, especially the SDE was very very annoying. I sold it via ebay after one week.
Then, I tried the Rift CV1 in December 2016 again, and the result was far better than with DK2. Nevertheless, I still couldn't get comfortable with the SDE. So, I brought it back to the vendor a couple of days later.
But... I got "addicted" And I discovered Pimax' 4K...
So, I bought my first Pimax just a few days later and received it in January '17. I played with it for almost two months regularly, then, the first "addiction" passed away, and the HMD lay next to me for another three months without being used. So, I sold it via ebay, too.
Well, when the prices for the Rift went down in June/July '17, I gave it another try. But still, the result didn't convince me. Now, especially, because the Rift's "black" in Elite:Dangerous isn't quite "black", but almost "grey"... And not to talk about the SDE, once again... So I gave it back, again.
But I noticed that I wanted to play VR again. And so, I ordered a 2nd 4k which is still with me - and since two weeks, in frequent use, again
For me, the 4k is the best VR-HMD at the moment, and that's why I have so much expectations concerning the 8k. Rift and Vive might be good for other people who are able to ignore the SDE and the greyish black. But certainly not for me - I can ignore much better the slight smear and the lack of brightness
So far - I really expect the 8k to to it better