I think Knight is more of a sure thing than Biyombo at this point. He did well throughout the season and was clutch for Kentucky in the tournament. He can do what Hornacek did for us - starting at the 2 guard position and back up PG when Harris is out.
Dont get me wrong I am in favor of drafting one player to start contributing in season 1 and the other to draft someone with "ridiculous" upside.