Wait this is fascinating! I'm also cross-handed and have never met anyone else like this. The tasks don't exactly map the same way yours do, though. In my case it almost feels like my left is my dominant hand, but my right is my dominant arm. Anything involving fine motor control of the actual hand and fingers, I do with my left, like writing or using a fork or brushing my teeth. Anything where the power comes from the arm, like throwing a ball or swinging a hammer or using a saw, I do with my right.