I understand that there are huge velocity ranges, but is there speed that would be a deal breaker no matter how good you are at other things?
No. There is not one speed or situation where a coach is going to say I'm not interested. There is more to pitching than velocity and I could rattle off a dozen or so things a college recruiter is going to look at holistically to make a determination if they are initially interested in a recruit. If you want an answer, I think you are going to have to ask the coach themselves and I really don't think that is a good question to ask. I think a better question would be to ask "what are the velocity ranges of your current pitching staff". So, this will give you an idea of the range across a typical college pitching staff of 17 players on a roster of 35 players.
There are many other considerations (movement, control, projectability, coachability, work ethic, frame, mechanics, etc..) across a wide variety of schools and situations. My son played with a pitcher (D1) who officially played exactly 1 inning in his entire 4 year college career beyond practice. He was a submariner and probably couldn't break a glass window with his fastball. He graduated with a 0.00 ERA. Do you know what he had going for him? He was very smart and his family endowed the Athletic Director's salary. He is currently in the front office of an MLB team. LIke I said, there are all kinds of considerations that schools look at. ;-)