I speak to a local D1 coach fairly consistently and she always focuses on movement and placement over speed. Her philosophy is no more than 20% fastballs and even that is high for her. Curve, Screw, Drop, Drop Curve, and a good rise every once in a while work well. Throw in a Change and you have a deadly mix (as long as they are placed well). Throw the fastball to seal the deal ever once in a while.
And you'll find that each college coach has their own opinion of what is effective, and what isn't. It all depends on what the coach believes, and what type of pitcher they are working with.
As far as different speeds, like between the fastball and changeup, the MOST important thing is that the changeup initially LOOKS just like a fastball at release to the batter. Then, the slower the better -
provided it does not drop too soon. Many really good changeups actually drop on the plate, with the batter swinging because they were fooled.
Speed differences also vary depending on the type of changeup thrown. A handshake changeup typically won't be as slow as a backhand changeup. I always liked the backhand, because it had to be thrown harder (with more energy), and that helped with the illusion of it being a faster pitch.
