I GREATLY prefer a straight 4' piece of trunk to virtually any limb wood. Try to cut pieces 6" or bigger.
Trunks spend their lives growing in a more nuetral state than limbs. Even if a limb appears 'straight', due to the natural forces of gravity, it grows resisting great tension on the top side, and great compression on the bottom which presents great challenges, often impossiblitites, to the bowyer. The transition wood to either side is even more unmanageable. It can be unpredictable, unruly and you may heat and bend it several times and still fight it throughout the construction process. Good bows 'can' be made from limb wood, but there's infinitely more junk in limbs than in trunks... even if only considering 'straight wood'.
As far as shorter trunk pieces, you can splice two 40" billets together at the handle and make awesome selfbows all day long that way. In fact, many folks prefer those to full length staves.
Don't rush to fill your garage with inferior bow wood(just because it's osage) like I did. Leave the limbs lay, or grow, and go find another nice short trunk piece. Often, when it comes to harvesting bow wood.... less is more.