Leland Roling of MMA-Analyst posted some strength of schedule statistics on BloodyElbow. He went two layers deep, and included the winning percentage of fighters’ opponents, as well as the opponents’ opponents.
Although his efforts were more than noteworthy, after taking a closer look, I felt the combination of the two layers was a bit subjective in nature. Furthermore, the statistics included the entire careers of all fighters involved, which I felt was overkill.
Update: Posted a Top 50 list.