I think if there was a direct correlation, of stride speed at the same stride length increasing velocity without any other negative effects, it would be very meaningful.
I actually believe stride speed will help produce more velocity. Just like a crow hop helps the outfielder throw with more velocity. But that stride speed needs to be under control.
My guess is that Randy Johnson had a fairly slow stride speed. Most extra tall pitchers do. Yet they are often the hardest throwing.
Trying to keep an open mind on the subject.