RSV: ... and of their race, according to the flesh, is the Christ. God who is overall be blessed forever. Amen.
NEB: ... May God, supreme above all, be blessed forever.
1. Christ's relationship to Israel on the human side has been stated in such a way as to call for a complementary statement on the Divine side.
2. The "Who" can only properly be coupled with the foregoing subject (Christ). If another subject (The Father) is being introduced there is absolutely no reason for the "Who."
3. A doxology to God can hardly be intended, since in doxologies, the word "blessed" is regularly placed before the One who is praised. Here it comes after.
4. A doxology to God would be singularly out of place in a passage marked by sorrow over Israel's failure to recognize in Christ her crowning spiritual blessing.
5. The definite article "the" is not linked in the text with "God" but with the foregoing words (literally: "the One being over all"). Paul, therefore is not trying to displace God with Christ, but is doing what John does when he says that "The Word was God" (John 1:1). This is what is really implied in recognizing Him as One who is "over all."