Thanks cobia and good luck on your bow!
I love hickory backing, especially with osage for the belly wood. Makes it pretty easy to put 3" of reflex in at glue up, or if you add a center lam of say elm, maple, walnut, etc., you can form it into a sweet shooting R/D tri-lam like Roy has been known to do.
I agree that you want the straightest grained board you can find. Last summer I bought two nice hickory staves. I'm just finishing a selfbow from one, but I saved the nicer, straighter one to cut into quarter sawn backing strips.