I've been arguing a lot recently, in the context of FIP and ERA, that looking at stats individually may cause you to miss details that looking at various stats together might reveal. Here is an interesting article by FanGraph's Jeff Zimmerman about xFIP and FIP: that deviations between from FIP to xFIP correlate--to a degree--to the average distance of fly balls allowed by that pitcher, with a higher positive deviation from FIP to xFIP indicating weaker fly balls (as you might expected due to xFIP's normalized HR component). Johan Santana is in the top 5 for starters (>160 IP) in this regard. What I'm more interested in, however, are the results of the questions for further study at the end, which might indicate whether this is really just a a matter of additional HRs or what.