Believe it is in fact somewhere in between - definitely not Full Array. That said, think about how you will use it - for me, I generally watch TV and Movies in my family room with some lighting on - I honestly don't think I could tell the difference 99.9% of the time between the 850 and the 900. If you are a video-phile who will place in a dimly lit home theater it may be worth the extra $$ for the 900 series.
My impressions of the 85" screen is that it is plenty bright with great viewing angles and controlled reflections. Both are great sets - for me, the $1.5K difference in price made it an easy choice to go with the 850. Good luck!