start here, and select a particular year then select Billings. It only goes back to 1992, I think
http://minors.baseball-reference.com...st.cgi?lid=PIO
this method can't tell you who will hit in the majors, because you'll get a lot of non-players that OPS pretty high in Billings. But it predicts who'll never hit in the majors, which is pretty valuable information.
maybe the reason that some of these guys never hit was due to poor developers-- batters had to at least be able to hit at a certain level coming into the organization, because we couldn't teach well. So if Stubbs becomes a hitter, it'll be a positive sign that things have really improved on the developmental front.