Until recently I considered w.elm and good ash to be quite equal material for heavy bows. I think different on the matter now. Not only does elm feel like it has a better "kick" from the same poundage, it also has a way of not developing compression marks before it's really poor tillered. Ash has a way of soaking water like a sponge, elm seems to be a little more tolerant to humidity. Both ash and w.elm seems to tolerate a lot of tension, but I have seen ash failing in tension. I've never seen w. elm do the same.
All in all I guess I'm on a quest of harvesting a lot more w. elm than I've bothered to do before.