Green has adequate speed but he runs like a big WR/athletic TE to me. His Nike 4.83 40 seems about right. He doesn't have really quick twitch moves and his "football speed", or change of direction ability isn't that impressive. Once he gets a head of steam, like Leidner, he will be a load to bring down. I guess it depends on the kind of player you like, a locomotive or more of an electric-type like Williams.
Of more concern, maybe to only me, is despite playing in a QB-friendly pure spread with 4 WR sets on the best team in Texas (with presumably decent receivers and an elite O-line) his completion percentage was in the mid 50s while his teammate Jonke was in the 60s.
Time will tell on him. Obviously we all want him to do well. Johnson will make his assessments on who will have the best success in his system, whether it's Croft, Green, or William, or the next 2017 QB recruit.