Mike Mayock during Cam Newton's workout. Said JaMarcus' was the best workout he had ever seen.
Regarding arm strenght, IMHO it's crucial for an NFL QB. Only a selected few have the accuracy and intelligence enough to make up for the lack of arm strenght.
And I'm not talking about the ability to throw the ball farther, or that the better the arm strenght the better the QB. But to thread the needle in the middle of the field, specially against zone, the QB has to have a strong arm.
All the elite QBs nowadays have it. Brady is supposed to be the weakest, but just look at his throws, first of all, he's the most accurate QB in the league (puts the ball in perfect position for his WRs to get it, away from the coverage, and in possibility for them to run after the catch. Rodgers is not very far, but Rodgers' short throws aren't as accurate). And the throws pop in the receivers hand. Yes, Brady can't throw backfooted, but that's not needed when I'm talking about arm strenght. Sure, it's great if the QB can, but a QB doesn't need that kind of arm strenght to succeed and even excel in the NFL
NFL Game Center: New England Patriots at Tampa Bay Buccaneers - 2011 Preseason Week 2
Click on his throw to 85 (not the TD) and you'll see what I'm talking about regarding arm strenght.
Now, there's no footage of it, but Greg McElroy doesn't have it. His medium and long passes take too long to reach the receiver. It might've worked in college, but in the NFL coverage is too tight, unless he has pinpoint accuracy, which he doesn't, he'll never be able to consistantly complete medium and long throws.
I don't think that's the case with Flynn. I believe Flynn has a bad tendency of not looking deep when faced with pressure, but that's not to say he can't consistantly complete medium and long passes. I believe he can.