The more camber gain you get with suspension compression, the less total contact area you have when the back end squats down during acceleration. This of course is ignoring tire flex which may compensate for this to an extent. A longer rear link will have less camber gain while a shorter link will have more. Theoretically this would mean a shorter link would have less straight line rear grip during hard acceleration but in practice that may not actually be the case. Camber link length will be noticed most in corners.