They will look at competition, the will look at combine results, they will look at measurables. Marquis Goodwin went high on speed alone at Texas and his production sucked and he's short.
Landry has great hands, physical and a great blocker. Quick footed and kinda reminds me of Antonio Brown but with better hands who Pittsburgh drafted in the 4th. If the production is there ala Randle 950+ 10TDs then I see him as a top 3 round pick.
Beckham is a perfect slot machine but I think also with his cone drill, 40 time, return skills, and competition, they will need to see production, YAC, and game changing moments in big games this year. He could go in the top 4 rounds if he has a 1000 yard type season but he'll need it to have a chance.