I only have the X4 and am very happy with it. As the resolution in particular is much higher, I would definitely go for the X4. You can find lots of comparison videos on youtube where you can see the differences...
I can't compare them, but I've watched a lot of YouTube videos about it and almost everyone advises you to buy the X4 straight away if you're buying a new one, as the video quality has made a huge leap due to 8K. That's why I bought the X4 straight away.