Go with the splice. 40” is very very short for a one piece self bow. 60” even is tricky if you’re not making a D bow. The top and bottom side of the branch are under different types of loads naturally, I would probably cut that branch down the middle where each billet will have both the top and bottom of the branch in it. It will probably give you some sideways warp as it dries, with a splice you could get a snake bow. If you cut it where the top of the branch is the back on one billet and bottom is the back on the other, I believe one will likely dry in deflex, and one in reflex.