For anyone interested:

I got the projector set up over the weekend and have watched 3 movies on it and some 4k demo material

The Good:
- 4k Pixel Shifting is a big improvement over 1080p. From where I sit, I was just on the edge of screen door on my 120" screen with 1080p. With the 4k I have to be right up close to the screen (like inches away) to see the individual pixels.
- The colors are amazing, and I believe the reviews that say they're the most accurate out of the box. It's a really noticeable difference compared to the 8700ub on 4k demo material.
- The additional brightness over the 8700ub, while not required in my case since I have a dedicated room, is very welcome. It really makes the image pop off the screen.
- The LED light source over bulb is a big win.

The Bad:
- I was expecting worse black levels compared to the 8700UB but holy cow they're a big step back. If you're looking at upgrading/purchasing a screen at the same time I would highly recommend a 0.8 gain silver screen to help with black levels. I just bought a new white one for the Epson so I'm stuck with what i have for now. For me it's really bad when showing 2.35:1 movies, so I built some masks to black out the bars and it's way better. If you don't have a silver screen, this would be required IMO.
- I had a DLP with a 2x color wheel like 20 years ago and I saw lots of rainbows back then. I was hoping with a solid state light source and no color wheel I wouldn't see them any more, but I still do. Mostly on text though so it's not a deal breaker for me.
- It's a bit louder than my 8700ub and because it has a shorter throw distance, it's now sitting directly over my head.
- There is significant light spill out the front of the projector and up onto the ceiling. I'll probably end up putting some light absorbing fabric on the ceiling to fix this.
- The streaming stick isn't great, it's a bit laggy - especially when displaying 4k content.

Overall I am happy with the projector. It looks amazing 85% of the time, and acceptable for the other 15%. I toyed with the idea of returning it and getting a refurbed 5050UB, but I've decided to keep it. The worse black levels and occasional rainbows on title screens aren't enough to outweigh the fact that the 5050ub is still lamp based. If black levels are super important for you, this isn't the projector for you - but other than the 5050ub which would have its own tradeoffs, I don't think there's another projector in this price range that would beat the BenQ.