The latest issue of Novum Testamentum has an interesting article:
J. van Nes, '"Faith(fulness) of the Son of God"? Galatians 2:20b Reconsidered' NovT 55 (2013), 127-139.
In this article van Nes argues for the P46 reading: EN PISTEI ZW TOU QEOU KAI XRISTOU and argues that these are both objective genitives ('I live by faith in God and Christ') which suggests that other Pauline pistis Christou references are also likely objective genitives.
This of course is not news to readers of this blog, since I argued for this reading in 2006 (here, with, as usual, some helpful discussion in the comments) [and the blog posting is noted on p. 132 note 17, and also on p. 137 note 38].