I'm sorry that I don't know more about him than I've read in boxing books or found on the internet. He also beat Holman Williams:

http://www.boxrec.com/boxer_display.php?boxer_id=009968

who was definitely an all-time great middleweight.

I suppose that Cerdan ranks pretty high among middleweights, maybe somewhere between #15 and #20. He would rank higher if he had fought more against other contenders, but like so many fighters of his era he fought most of his fights against beginners and bums.