I have an X850E and couldn't be happier. In my personal side by side viewing between that and the X900E, there is a slight difference in brightness at the 65 inch level but not enough to justify paying an extra $500. They both looked better than the 2017 8000 series from Samsung. The 75 inch X850E is an IPS panel though, so the blacks look washed out. I would only buy the 65 if you are going the 850E route but I don't like IPS panels very much.
The feature set is outstanding, and the remote even works on your PS4 which is convenient. It has Bluetooth so it connects easily to your headphones for private listening which is awesome. Android tv can get a tad sluggish from time to time, but it's not enough to outweigh all the positive features on this one in my eyes. It has every app you can think of plus chromecast built in.
Honestly, I haven't been happier with a TV in a long time and it was right at my 1500 budget for a new bedroom/gaming TV.