Lacy has been coming off a hamstring tear, so it is pretty hard to stay in top condition when you can't run. I can't imagine the 4.4 times are correct. He ran a 4.4 last year at his Junior Day, so he does run that fast, but there is no way coming off a hamstring tear and sitting on his butt for three months, would be be able to do that. No chance.
So, I tend to believe Bucky Brooks on this, though I think Bucky is a moron if he thinks any team will downgrade Lacy because he's not in top condition. There was no way he could have been.
Regardless, if he ran in the 4.5s with the still lingering injury and not being in top shape, that's impressive. His speed is the least impressive thing about him anyway, his agility, vision, and overall game is what stands out.
I think this is best case scenario for the Broncos. If he blew up this Pro Day, he wouldn't make it to us. Now there's a chance at least. I think anyone that broke down his game tape would be thrilled for us to draft him. Even with RB being a diminished position.