I juuuuuust answered this question for myself. WTB Nano 700x40 was what I purchased. At first, I got the Kenda Slant Six 700x32 and Happy Medium 700x32, but the UCI limit width 32mm is a little small for comfortable off road trail use. The 40mm is perfect.
I only considered "SCT" type tires, the ones made specifically for tubeless. There are non-tubeless versions of each of the above tires.
The Nano tread pattern is pretty fast on dry hardpack and gives good grip in the loose stuff.
I run them at 25-30 psi @ 70kg with no problems. I could go lower, but I hate bottoming out my rims on rocks.
Tubeless sealant I'm using is 40% latex, 30% propylene glycol, 30% water.
The Nanos are 100mm bead to bead. 35mm width on 15mm id rim, probably 41mm on the Ardennes +.