"Grace of Christ" in Galatians 1:6

Today I did some text critical work in Galatians 1:6-10 for the Galatians commentary. I'm going to discuss three problems total for this paragraph; the most interesting one in my opinion is the one which occurs in v. 6. Here's the text of v. 6 from the NET Bible and then the discussion I plan to include in the commentary on the textual problem. 

I am astonished that you are so quickly deserting the one who called you by the grace of Christ and are following a different gospel.

The reading ἐν χάριτι Χριστοῦ (“by the grace of Christ”) shows multiplied variation in the mss; it is the best candidate for the original reading, but the variants are theologically interesting. Two readings appear to be expansions of shorter readings and can be readily dismissed: The reading ἐν χάριτι Ἰησοῦ Χριστοῦ occurs in D 326 1241s pc syh**. This variant is minimally attested and very likely a scribal expansion on the shorter reading ἐν χάριτι Χριστοῦ. The reading θεοῦ in 327 pc and Theodoret of Cyrrhus is also minimally attested and would appear to be a scribal expansion of the shorter reading ἐν χάριτι, likely in harmony with Paul’s numerous statements elsewhere which connect grace to God (Paul only consistently speaks of the grace of Christ in letter conclusions). The strongest variant is the shortest reading, the omission of the name Χριστοῦ in P46vid F* G Hvid ar b and some Church fathers. This reading is exegetically equivalent to the reading ἐν χάριτι θεοῦ; if no name were present most likely grace here would be connected to God. This reading fails, though, on the weakness of its external evidence, supported by only part of the Western text. The reading of the NA28 text has strong support from Alexandrian and Byzantine mss, and so should be judged to be original based upon external evidence. It is also the harder reading in that it is out of keeping with Pauline style. Thus ἐν χάριτι Χριστοῦ best explains the rise of the other readings and should be judged as original.