I just finished a hickory pyramid bow that pulls a nice 45# at my 26 inch draw.
Like others have said, it's all about avoiding the grain run-outs ON ALL FOUR SIDES. If you are making something with a stiff narrowed handle, you will want to glue on a little builder-upper on the handle and fade out section, but 3/4 inches of hickory meat is more than enough to make a bow heavier than your shoulder (or mine for that matter) wants to pull!!!
If you live in a dry climate, the hickory will probably outperform the ash. But both will suffer from humidity, hickory just hates to give back any moisture it sucks up from the environment, greedy stuff that it is!
Go for it! Post pics as you go!