The oak bows I have made (one white oak, two red oak-both boards early in my learning process) all took quite a bit of set. It could have been me, but I think that is pretty normal with oak. The backing should help a lot. keep it wide anyway, and it will make a good bow. If you want curves in the tips, I would steam them in, set them with dry heat, and then back with the maple that has also been steamed to shape.