What I saw last summer Northern California 10u-B was:
Fast= 47+
Above Average = 45-47
Average= 41-44
Slow = sub-40
Saw one girl consistently throwing 48/49. About half the teams had someone throwing 46/47. To be competitive, you had to have someone at least throwing 43/44.
Agreed. However, it's shocking how effective a sub-40 pitcher can be against a team used to seeing 45+ - LOTS of weak ground balls. Slow pitchers with location control can be extremely valuable in relief.
Been on both sides of a girl who only could pitch 35-37, but had good control. With a good defense behind her its definitely worth pitching her once through the line-up as a relief pitcher or starter. Good hitters at 10u (and sometimes 12u) have trouble adjusting to slow pitching when they are used to mid-40's or faster.