389 broke 3:52 in the 1500m (roughly 4:10 mile) outdoors this year and
224 broke 4:09 in the mile indoors (33 broke 4).
303 broke 14:30 in the 5000m (79 broke 14).
Obviously, even excluding foreigners, there is a lot of improvement in D1 college.
In D3, only 20 broke 3:52, so the lack of competition in practice and/or talent and coaching are limiting the development of D3 runners, but 180 broke 4, which converts to about 4:18 mile, so that is a pretty solid figure, considering that most sub 4:20 milers in high school are going D1. 500 broke 4:07, about a 4:25-26 mile, so D3 has at least a lot of guys ahead of the proverbial high school 4:30 miler.
In the 5000m, 21 D3 athletes broke 14:30 (1 at 13:51 broke 14), 145 broke 15, pretty solid, 420 or so ran 5:00 mile pace or better for the 5000m (15:32.3 or so). I would bet that many D3 athletes would improve more in D1, because the best guys on a D3 team are not typically going to have sub 14:30 guys to train with.