I'd say that without his injurys Ledley could have been world class he had the knowledge and the ability to have played for any of the top teams. We can be sure that had he been fully fit offers would have been made whether he would of accepted them we will never really know.
On his day, Ledley was world class even with his injury. Without doubt amongst the most talented CB's to ever wear a Spurs shirt.
My feeling is that if he had stayed fit, and become an England regular, we would not have been able to hold onto him.