My wife and I both use Velocity Dyad rims, Wheelsmith double butted spokes and either XT, Ultegra, or 105 hubs. The XT and Ultegra hubs have the most miles. On a tour in 2011 part of our route took us over 400+ of dirt roads and trails, and 500+ of cobbles and sett paving. Both wheels held up very well. A well built 36 spoke wheel will hold up amazingly well.
As I said in an earlier post: Co-Motion uses the Dyad rims on their tandems, touring bikes and on the "Americano" their expedition bike. Take a look at the specs on their wheels, and you will probably have good idea what a quality built trekking wheel will look like.
However, I do think the Mavic 719 rims may be a little more rugged. The reason I didn't go with the 719 is that they are a little heavier.
I don't know about the WTB SX 19, but I ran a pair of WTB DX 23's (32 spoke)on my CX bike. The wheels had a lot of hard use, including a ride across the U.S. They are the only touring wheel that I ever broke spokes on, all on the front wheel. I think the fault was the result of an over-zealous shop mechanic when he trued and tensioned the wheel. I broke three spokes within a week, right after they were worked on.
Last edited by Doug64; 03-22-15 at 05:27 PM.