Ribery does not have sheer speed, but rather acceleration. Besides I seem to remember Paulo keeping Bale in his pocket in two different matches. Wither way, who ever plays at RB will need help from the winger to stop Ribery, and same goes for robben on the other side. It will take a team's tactic more than an individual defending skills. It's just that Paulo is much more reliable and less like to commit costly errors.