My playing days are pretty much ended now (in my mid 40's) but I played a ton of pick up ball at the U and played adult men's league ball until last year. My experience, having played with and against quite a few former D3 and D2 players and getting a few reps in against the Gophers back in the day, is that the biggest difference between a D3 and D1 player is athleticism. The D1 player is almost always bigger, faster, stronger. The D3 player might be just as good if not a better shooter, but athletically they can't match up against a D1 player. So if a D3 player has size and athleticism they would be more able to make that jump from D3 to D1.