First, here are his overall AVG-OBP-SLG from 2008-2013 (which includes games against both the AL and NL)
Now what he has done in inter-league games from 2008-2013, over 466 PAs
I used the Baseball Reference Play Index and called up his plate appearances against all the NL teams, including the Astros, so this includes how he has hit against them this year (in 34 PAs .379-.471-.759). So it seems like he has hit better against AL pitchers and that although it is not a huge difference, it is clearly noticeable. It is surprising because over this period the AL has been winning most of the inter-league games.