His floor would be Lamar Jackson. Justin Fields has all the speed and athleticism as Lamar with additional size. All he has to do is be a mediocre to average passer.
His ceiling would be redefining what a prototypical QB is. Along with size, speed, and athleticism, he has great arm talent and a good head between his shoulders. He has the potential to be the most complete QB ever.
He's been compared to Wilson and Prescott, but he's quicker than both of them. Justin Fields is also bigger than Wilson, which allows him to make throws that Wilson can't. I also think that he has a stronger arm than both. If Justin Fields can pick up the game, he should be able to surpass these QBs. Some say he could be as good as Mahommes, but Justin Fields has better speed and mobility to go along with similar arm talent. If Justin Fields picks up the ability to read defenses and consistently find open receivers to go along with his ability to burn the defense with his feet, he'll surpass Mahommes. Some compare him to Rodgers because he could extend plays with his feet, but he wasn't a guy that could break a long play with his feet either like Justin Fields. I like the comparison to Steve Young, but even still Justin Fields is bigger, faster, and has a stronger arm.
I have watched the Bears faithfully for over 40 years. Never, ever, had I been excited about a prospect, let alone a QB that the Bears have drafted or signed as much as I've been about Justin Fields. I have groaned at many picks and signings, and have seen plenty of training camp and preseason heroes over the years. Justin Fields is the only QB drafted that I think will be a real deal franchise QB.