Fleet also ran a 3:50 1500 (as a Soph!! Where he won against college comp. Greer came in 4th or so).
Fleet ran a 1:50 800 last year, that's 3 seconds behind Greer, but he was coming off a foot injury and was supposedly 20+ pounds overweight (6-2 185 instead on 160-165). He was very inconsistent last year compared to his Soph year. He never really seemed to round out into shape - probably due to his lack of base.
So I'd put his odds close to or equal to Greer's.
Fleet would have to come down 8 something seconds from his indoor time. That seems a tall order, but then again he is tall and indoor is probably not his best surface. He is also supposedly doing all base right now.
If he stays healthy and gets in the right race, he should be able to break 4:05, by how much...????
Sub 4:00 seems unlikely, but not impossible. He has the speed and his times as a Soph seems like he could make that amount of progress. I would not bet on it, but it would not shock me.