He's a small school guy and not the best slot CB right now... but he has amazing quickness and tons of upside. Should be great value too as a late 2nd, early 3rd round pick.
Past Dee Milliner, there aren't many big CBs that can really move with quick WRs like the guys you mention. You kind of have to compromise and go with a smaller guy.
Did I mention Webb has a 40" vertical??? Helps make up for the lack of height