I think he was A- caliber. Gotta know he ate up alot of mexican fodder to rack up his record. Never the less, he was a natural puncher who stayed in the pocket. I generally call him a lousier version of Pacquiao w/o the footwork. I think Marquez would dismantle him, considering he's a phenomenal punch technician and Valero didnt move too much.
Sky is the limit, IMO he would have run rough shot Vs. any and ALL current Lightweights. (Yes, Even agaisnt JMM)