Well, he could have done it this way: I'll attack Oro, if I lose, he gets my body and goes for Itachi (eventually), if I win, then I am better off going after Itachi since I'm stronger. But the logic unravels since Oro isn't healthy right now. So maybe he planned this from the start. It's about time Oro changes his body, so it's now or never. If he waited, Oro would have got some other body and would probably beat him.