The odds that my comments here -- more than a year after the last comment -- will be picked up by you previous commenters are slim. I have a few observations on this passage, and Romans six through eight in general. First, in the 40 years I have carefully studied these chapters, I have been continually amazed at how many good teachers and scholars seem to struggle with letting Paul say what it seems plainly he is saying.
I know that often scripture doesn't mean what it appears to mean on the surface. I think there is a common tendency to miss the ontological sense in which Paul is speaking when he says things like we are in the Spirit and not in the flesh, or in Romans 7:17,20, when he says that it is no longer we who sin!
I wonder if our theological traditions cause us to fear taking these passages for what they seem plainly to be saying. It is such a profound subject Paul is dealing with in those three chapters that even if we move more towards what I am talking about, it is mysterious territory. One of the big challenges is that we have to discern when Paul is speaking ontologically and when he is speaking experientially -- speaking about visible earthly appearance and performance.
That is, we need better perception of when he is speaking about who we now are organically and, according to God's perspective, literally as brand new creatures in Christ, where the old has in fact, passed away and the new has come ... and when he is speaking about our earthly experience and visible expression as spiritual beings still walking around in dead, unsaved physical bodies.
By the way, the one reference cited by the OP in footnote 7 above is erroneous when it comes to Galatians 2:20. The Greek word is not sarx, but soma. Most translations say "flesh" when they should say, as the NIV amazingly does, "body". I love what John MacArthur said one time in his teaching on the mystery of being "in Christ", expressed in Colossians.
He said that he is asked, Why, if, as he teaches, we are brand new creatures in Christ ... why do we still sin? His answer is spot on. We still sin because although we are brand new creatures, born again, we are walking around this earth in dead, unsaved bodies, where the law of sin is still at work in our "members".
If you do a careful study of exactly what Paul says the source of sin is in Romans chapters 6 through eight, you will see the repetition of the words body, body of sin, members, members of my body, and flesh. This completely supports what MacArthur said about our earthly performance in spite of being brand new creatures in Christ who are no longer in the flesh.
In fact, we were circumcised, according to Colossian 2:11-13, by an amazing, miraculous circumcision where Christ severed us from the flesh and literally regenerated us in himself such that we are now hidden with him in God until the day he comes and reveals himself and us in him! (Col 3:1-4) That Colossians 2 passage is definitely one where we have a hard time letting it say what it is saying, but it is perfect commentary on Paul's discussion of the radical transition that has taken place for the man in Christ, the moment he was saved, seen all through Romans chapter six, seven, and the first part of eight.
I could summarize all this by simply saying that "in Christ" may be the most undervalued and dumbed-down phrase in all of Scripture, especially when it comes to understanding who we now are as brand new, regenerated people.