With RB's and WR's, I want to see them run fast, show burst in the 10 and jumps, or show really good agility for their size. I think it's a little similar for LB, but raw speed, relative to their size, is more important for them, with the way teams spread the field.
I agree about pass rushers and DB's. Pass rushers and CB's are typically the best athletes on the field. With Safeties, I think it's more similar to RB and WR. They need to be decent all-around athletes and to have a good trait or two, but anticipation and instincts seem to go further. Anything over 4.60 is a red flag/knock, though.
Chubb is a great call. I agree that if he shows burst like he did in high school, top-50 is on the table. I always loved his game. I made a list this morning, and I didn't focus as much on RB or WR, but of those positions, I also really want to see Penny, Freeman, Kelly, Johnson, Walton (though, I won't hold a bad performance against him), and Adams at RB, and I want to see Sutton, Gallup, Moore, Ishmael, and Wilson at WR. I left of Ronald Jones II, because I feel confident that he'll test well. This is the list I made earlier (not concerned with Bradley Chubb):
OT
Connor Williams
Jamarco Jones
Orlando Brown
Chukwuma Okorafor
Pass-rush OLB
Harold Landry
Marcus Davenport
Olasunkanmi Adeniyi
Dorance Armstrong
Josh Sweat
Obo Okoronkwo
Uchenna Nwosu
Stand-up LB
Roquan Smith
Tremaine Edmunds
Leighton Vander Esch
Malik Jefferson
Christian Sam
CB
Derwin James
Minkah Fitzpatrick
Carlton Davis
Isaiah Oliver
Jordan Thomas
Jaire Alexander
Darius Phillips
Mike Hughes
Denzel Ward
DJ Reed
Duke Dawson
MJ Stewart
Jalen Davis
Arrion Springs