As some allready have mentioned, ash can vary from average to excellent. The European ash is better than the american in average, but you may find good pieces of american ash just as easy as you find bad european ash. Look for ash who favors the late growth rings by as much as possible over the early growth rings.
Without heating the belly, I've seen ash ELB warbows successably made up to 130#@32". (Rare good piece of local ash, grown here by the lake Mjøsa).
With good and thorough heat treatment of the belly, I guess 170# from a good piece should be possible. Maybe more. (You've given me a quest on testing it's limit here
)
One of the most important things to know aout ash though, is how it likes to soak humidity like a sponge. Remember to add the closest to waterproof finish you can find. Humidity kills pondage in heavy bows.
With "malming" of the belly, I guess I may try to hit 200# with ash... But I'll note it in the back of my head for an experiment later. Right now I'm working on a 190# wytch elm snaky sapling bow for Joe Gibbs. I'll post it once it's done.