You'd have to look at it from the other angle also, what is a pitchers success with said pitch? To Yoda's point, a batter sees a bunch of hanging breakers, but what if it's off a dude who's curve has a .400 BA against it because he hangs it every time? Even if it's his 4th pitch and the only reason he throws it is so the batter has something else to think about?
Just saying, look at both sides of the equation. Making up some random #'s, if Melvin Mora hits .385 swinging at two-seamers, and Beckett's two seamer has a .209 BA against, which side are you taking with a mortgage payment on the line?
Good luck though, and let us know if you find anything, I'd be interested.