Sounds like springing for the X90J at the enormous discount I got it at was the way to go!
I wouldn't get too cut up about the reflective coatings tbh, the X90J handles reflections fine in our brightly lit room and a downwards 5 degree tilt meant it no longer caught dimmed lights at all. I can understand it for things like the Frame TVs which have to be wall-mounted flush against the wall, but for something you can tilt generally tilt away from, it's not a deal-breaker.
If the X90K is similar (and has higher native brightness) then that's an easy sell.