The 90 degrees rule applies to the Hobie 16, I don't know about other cats. On the downwind leg we go with 90 degree of apparent wind, then set the jib accordingly (in lighter wind the crew has to hold the tack with the hand in order to induce more bend in the battens) and now we steer by the jib telltales (never ever stall). If we note we are going higher than 90 degrees with the lee telltales just before stall, the jib as to go out more. So it really is a combination of the two. Remember, the jib is it all for going downwind.