I'll wade in on this one, Raff.
I've cut some healthy looking trees that had no useful timber, and some very dead elm/cedar/cherry/oak/ash/hemlocks with great wood inside. I think that the more resistant woods are the ones with the best standing dead wood.
My understanding of the dutch elm disease is that it is carried by a beetle of some kind or another. So elms in groups which already show the disease are pretty much doomed. Solitary elms seem to do the best.....
