You're not going to find many CB's coming out faster than Robinson. As for size, look at the top rated CB's to come out the last few years--Newman, Hall, Robinson, Jammer, Buchanon--Jammer is the tallest at 6'. WR's have a huge advantage in that they know where they are going. DB's have to react to what the WR's do, and with an emphasis on no contact, they can't do it by bump control anymore. One of the best assets for a CB is short distance closing speed. It seems that it is much rarer for the taller players to have the reactions and closing speed to be great cover CB's. There are a couple of 6' 1" guys coming out next year.
The Art of War