I use the 1000x Lexar (32 Gb) with my D800 and so far it's been brilliant. I don't think you need to worry - its absence from the manual is probably a question of timing (i.e. cards not available when the manual was written).
Enjoy your D800 - it's awesome!
D4, D800, D600
It ain't so much the things we don't know that get us in trouble. It's the things we know that just ain't so.
Why is this thus? What is the reason of this thusness?